The reasons for the yield enhancement effect of the ovicide chlordimeform [N(1)-(4-chloro-0-toly)-N-N-dimethylformamidine] in cotton (Gossypium hirsutum, L.) have not been fully elucidated. Our objective as to determine the effect of foliar applied chlordimeform on stomatal conductance, transpiration rate, and apparent photosynthesis of the three uppermost fully expanded leaves of cotton during the developmental stages when yield enhancement applications are made.