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Two monoclonal antibodies (16 D3 and 24 E3) were used to map tubulin domains in human spermatozoa by indirect immunofluorescence. Their specificity to tubulin in these cells was established by Western blotting. Whereas 16 D3 uniformly stained the principal piece of the flagellum, the staining provided by 24 E3 decreased along the tail to become very weak 30 micron further away from the midpiece. This latter antibody also reacted with the proximal centriole as well as the midpiece, but not all spermatozoa stained identically at this level indicating heterogeneity within the population of sperm cells from a given donor. 16 D3 reacted weakly with the head, and the staining was interrupted after a bright spot in the neck. The study of a pathological case (the short tail spermatozoon) with an abnormal arrangement of dense fibers was consistent with a correlation between the distribution of the epitope defined by 24 E3 and that of peri-axenomal structures. The existence of tubulin domains interacting with these structures is postulated.