The morphology of T-mycoplasmas in culture and in semen from men of infertile marriage was examined by scanning electron microscopy. In cultures obtained from semen of infected individuals, T-mycoplasmas were recognized as spherical particles, 160 to 200 nm in diameter, frequently interconnected by short, straight fibrils. Numerous T-mycoplasmas and associated fibrils with similar morphologic characteristics were also observed adhering to spermatozoa obtained from ejaculates of the infected donors. Similar granulofibrillar aggregates were never observed on control specimens. These observations indicate a physical association between the microorganisms and spermatozoa in semen of infected men. This association may contribute to the decreased motility of spermatozoa in semen from which T-mycoplasmas can be cultured. The binding of T-mycoplasmas to human spermatozoa may provide an effective mechanism for transfer of the microorganisms past the normal microbial barrier of the cervix.