Inoculation studies with Penicillium cyclopium isolated from spoiled, ripe mangoes showed that the degree of infection in whole fruits increased with ripeness. Factors that could render an unripe mango less susceptible to infection by this mold were investigated. The mold grew optimally at pH 5·0. Citric and malic acid at concentrations present in the unripe fruits partially inhibited its growth and increasing concentrations of glucose and fructose had a stimulatory effect. The mold was able to utilize starch. The levels of pectin lyase, cellulase, amylase and invertase increased upon infection. The total carbohydrate content decreased upon spoilage, while the total reducing sugars increased. The levels of glucose increased on spoilage but fructose levels decreased.