Reproductive tracts and spermatozoa from reproductively active and reproductively suppressed non-breeding males from two species of eusocial African mole-rats Cryptomys damarensis and Heterocephalus glaber were examined. In two captive colonies of Heterocephalus glaber, reproductive tracts from seven non-breeding males removed from their colonies, and housed singly for 5-6 weeks to cause reproductive activation, were compared with reproductive tracts from seven non-breeding males. The body weight of the separated, reproductively active males increased significantly (P < 0.01), and the mean testis weights relative to body weight of the reproductively active males were significantly larger (P < 0.05) than those of non-breeding males. The number of spermatozoa, in one half of the reproductive tract, was higher in active males than in non-breeding males (mean +/- SEM: 8.59 x 10(6) +/- 2.69 x 10(6) versus 1.78 x 10(6) +/- 1.43 x 10(6), respectively; P < 0.05). In addition, six of the seven reproductively active males, but only two of seven non-breeding males, had motile spermatozoa. A total of 28 wild Cryptomys damarensis from two colonies were examined in the field. The testis weights relative to body weight of breeding males (n = 7) were higher than those of non-breeding males (n = 19; P < 0.01), but the number of spermatozoa did not differ significantly between the two groups (0.13 x 10(6) +/- 0.06 x 10(6), n = 7 versus 0.29 x 10(6) +/- 0.14 x 10(6), n = 21, respectively). Breeding and non-breeding males produced similar numbers of motile spermatozoa.(ABSTRACT TRUNCATED AT 250 WORDS)