Several factors appeared to have influenced the individual mother's decision about infant feeding: economic situation, family size, reported ability to produce breast milk and advice received concerning breast milk. Exposure to commercial advertising and women's participation in the labour force did not emerge as determining factors in the infant feeding decision of the women studied. The decision to breast feed taken by exclusively breast feeding mothers appeared to have been influenced by the conditions of poverty in the households. These mothers may have made the decision to breast feed due to a lack of economic alternatives. Concurrently, breast feeding mothers received considerable advice and encouragement to breast feed. Formula feeding was not limited to mothers in households having higher incomes than the rest of the sample studied. Over 50% of women using formula or other milks to feed their infants lived in households receiving the median or lower incomes in the community. For women unable to nurse, the decision to feed with cow's milk, powdered milk or a commercial formula was the only viable alternative. It has been argued that if commercial milk formulas were not widely available to Third World women, breast feeding would flourish. This assumption was not confirmed by the data obtained in the present research project. If no breast milk alternatives had been available to mothers who reported lactation failure, their infant feeding problem would have been compounded. At the same time, it can be seen from the data concerning monthly cash expenditure for milk that the most economically disadvantaged women who purchased milk needed to spend an inordinate amount of the households' income for that item. The decision to formula feed in these households put a great strain on the family's income. In the case of women who formula fed, family size may have been a determinant in the feeding decision. More formula feeding mothers had from 5 to 10 children than did breast feeding mothers. The demands on the mother's time due to large family size and the convenience of allowing an older child to bottle feed the infant may have made milk or formula feeding a more attractive alternative to these mothers. Perhaps more importantly, the effect of a greater number of pregnancies and childbirths on these women's health may have contributed to their reported inability to nurse the most recently born child. Knowledge of influential factors in the mothers' infant feeding decisions could be used by nutritionists promoting education programs in rural areas such as Malinalco. Before breast feeding is generally recommended, mother's capacity for lactation should be investigated. In the community studied, formula feeding women often depended on the experience of others in choosing a type of milk for their infants. In many cases it was only after an inappropriately chosen milk had caused diarrheal disease in the infant that the mother visited the physician and received advice. A more accessible health care system, of which nutritional counselling is a part, needs to be made available to women in these situations. Optimally, an inexpensive milk formula could be distributed to these women through government subsidized health clinics. While intervention programs may be needed in poor rural communities such as the one studied, they cannot deal with the overall situation of poverty which contributes heavily to disease and death of infants in rural communities in the developing world. Presently nutritionists may not be working closely with economic planners in Third World countries to correct situations which are damaging to infant's nutritional status. However, the effects of poverty and the specific ways in which they condition mother's feeding decisions will have to be taken into account if infants in developing nations are to be better nourished.