Semen samples (91) from 47 vervet monkeys were collected by electroejaculation over a 2 year period. Seventy-eight of these were from 37 singly caged males of unknown fertility and 13 from 10 breeding males of known fertility. Mean values for semen characteristics of the singly caged males were: volume 0.45 ml, pH 7.8, concentration 184 x 10(6)/ml, forward progression rating 2.95 (scale 0-4), motility 55.4%, live 68% and abnormal morphology 3.5%. Mean values for semen characteristics for the breeding males were: volume 0.86 ml, pH 9.00, concentration 117.15 x 10(6)/ml, forward progression rating 3.00 (scale 0-4), motility 43.6%, live 53.3% and abnormal morphology 6%. Semen volumes in the singly caged males were lower than the volumes reported in other studies.