Ten-week-old male Sprague-Dawley rats were injected i.p. with cadmium chloride solution in a single dose of 0 or 1.0 mg/kg BW. At 4, 24, 48, and 72 h after injection, testes of the animals were collected, detunicated, and fixed in 10% formalin. Individual seminiferous tubules were isolated and the stages of the cycle of the seminiferous epithelium were determined through use of transillumination under a stereomicroscope. The tubules were stained with rhodamine-phalloidin, mounted on glass slides, and examined via a confocal microscope. This cadmium dose did not cause visible vascular lesion in the testes. The cadmium treatment resulted in changes in the pattern produced by microfilaments in the basal region of Sertoli cells. The observed change in basal Sertoli cell microfilaments consisted of fragmentation of the microfilament bundles as compared to those in seminiferous tubules from control animals. This apparent lesion was first observed in stages VIII through XI at 24 h after the cadmium exposure. As the time after exposure increased, the lesion within a stage occurred with increasing severity, and later stages of the cycle of the seminiferous epithelium were also affected. At 48 h after exposure, disorganization of microfilament bundles was seen in stages VIII through XIII/XIV. At 72 h after exposure, severe fragmentation of microfilament bundles was observed from stage VIII through stages II/III. The microfilament bundles in several stages prior to stage VIII remained unaffected. No change was observed in the microfilaments of peritubular cells. At 4 h after exposure, testes showed no change in the organization of microfilament bundles at the basal region of Sertoli cells or microfilaments in the peritubular cells. We conclude that a single cadmium chloride dose of 1 mg/kg results in the disruption of basal Sertoli cell microfilament bundles in the rat seminiferous epithelium, and that the action of cadmium is cell-specific and stage-specific.