Three cotton cultivars (Gossypium hirsutum L.) were grown in sand culture in a glasshouse. The nutrient solution contained no or additional sodium chloride (43 or 86 mol m−3) and overall had electrical conductives (ec) of 1.4, 4.0 and 6.6 mmho cm−1. Cotton yield was lowered by salt but lint percent was increased. Fibre properties were lower in one group of plants, which flowered and were harvested later, than in the other, earlier group. Cotton raised at high ec values were shown to have a higher sugar content but decreased cellulose content. The fibers were thus of reduced maturity. Since fibre perimeters appeared to be unaffected, it would seem that the immature fibres would be lighter and weaker than their counterparts, and that this would explain the fact that micronaire values, linear density, maturity percent and ratio were all found to be lowered at high ec values. Similarly, moisture-regain values were increased. Attachment strength of the lint to the seed was also reduced at high ec values, although it is less certain that this was due to reduced cellulose content. The results show that both yield and quality of cotton can be affected by increases in electrical conductivity, and that the quality is probably related to decreased maturity of the individual fibres.