The present work provides an assessment of sperm measures (concentration, motility, viability, etc.) of three black-handed spider monkeys (Ateles geoffroyi) during the rainy and dry seasons in Mexico City, as well as an evaluation of the between-subjects variability of sperm quality. Twenty samples obtained by rectal electroejaculation and digested with trypsin were evaluated. The results showed that during the dry season (n = 9) the semen samples were of better quality than those obtained during the rainy season (n = 11). The individual animals showed differences in sperm concentration, although there were no differences in sperm quality. Am. J. Primatol. 57:35–41, 2002. © 2002 Wiley-Liss, Inc.