Reproductive data are presented on Myotis nigricans from the Panama Canal Zone and Mexico, Myotis albescens from the Canal Zone and Peru, and Myotis simus from Peru. Spermatogenic activity in Myotis nigricans occurs continually from December through August in the Panama Canal Zone. From September through November most males are in a resting stage with regard to spermatogenesis, and copulation was not observed during this period. Females undergo a similar cycle, resulting in few young reaching foraging age during the dry season (January to March). Males reach sexual maturity at an age of 3½ to 4 months. Photoperiod is suggested as a possible environmental cue for the cycle. Data from Myotis albescens and Myotis simus suggest a reproductive pattern more similar to temperate zone species.