The safety and spermatogenic activity of processed Shilajit (PS) were evaluated in oligospermic patients. Initially, 60 infertile male patients were assessed and those having total sperm counts below 20 million ml(-1) semen were considered oligospermic and enrolled in the study (n = 35). PS capsule (100 mg) was administered twice daily after major meals for 90 days. Total semenogram and serum testosterone, luteinising hormone and follicle-stimulating hormone were estimated before and at the end of the treatment. Malondialdehyde (MDA), a marker for oxidative stress, content of semen and biochemical parameters for safety were also evaluated. Twenty-eight patients who completed the treatment showed significant (P < 0.001) improvement in spermia (+37.6%), total sperm count (+61.4%), motility (12.4-17.4% after different time intervals), normal sperm count (+18.9%) with concomitant decrease in pus and epithelial cell count compared with baseline value. Significant decrease of semen MDA content (-18.7%) was observed. Moreover, serum testosterone (+23.5%; P < 0.001) and FSH (+9.4%; P < 0.05) levels significantly increased. HPLC chromatogram revealed inclusion of PS constituents in semen. Unaltered hepatic and renal profiles of patients indicated that PS was safe at the given dose. The present findings provide further evidence of the spermatogenic nature of Shilajit, as attributed in Ayurvedic medicine, particularly when administered as PS.