We describe the results of meiotic and synaptonemal complex (SC) studies in a selected series of 45 subfertile males with different meiotic and seminal alterations. SC anomalies (pairing anomalies, fragmented SCs, or presynaptic arrest) were observed in 32 cases (71.1%). In 31% of the abnormal cases, meiotic anomalies could only be detected through the study of SCs. The origin of synaptic anomalies may be related to the assembly of myosin molecules along the chromosomes. SC analysis should become routine in the study of subfertile males. © 1982 Springer-Verlag.