This study concerned the minimum and optimum effective doses of calcium chloride needed for induction of chemosterilization in male albino rats, 30 days after a single intratesticular injection of calcium chloride (CaCl2.2H2O) solution at 2.5, 5, 10 or 20 mg per 100 g body weight per testis. There was a significant diminution in the relative wet weight of the sex organs (p<0.01), epididymal sperm count (p<0.001), plasma concentration of testosterone (p<0.01), testicular activities of delta5,3beta-hydroxy steroid dehydrogenase (delta5,3beta-HSD), 17beta-hydroxy steroid dehydrogenase (17beta-HSD) (p<0.01), glutathione S-transferase (GST) (p<0.01), superoxide dismutase (SOD) (p<0.01), and peroxidase (p<0.01), significant elevations in testicular content of malondialdehyde (MDA) and conjugated dienes (p<0.01), along with derangement of seminiferous tubular architecture and degeneration of the Leydig cells in the testis and elevations in the concentrations in the plasma of LH and FSH (p<0.01), commencing at a dose of 5 mg, with the greatest effects at a dose of 20 mg. No significant alterations in these factors occurred at the dose of 2.5 mg in comparison to the control that received only the vehicle. There was no significant alteration in the plasma concentrations of prolactin (p>0.05), corticosterone (p>0.05) or fasting blood glucose or in the rectal temperature (p>0.05) at any of the doses relative to the control group, suggesting that this chemosterilizing procedure did not exert any chronic stress on the experimental animals. From these observations, it may be suggested that 5 mg should be considered as the minimum dose, and 10 mg or 20 mg as the optimum dose, whereas 2.5 mg was ineffective for induction of chemosterilization. There would seem to be little point in using more than 20 mg of calcium chloride for this purpose. Intratesticular injection of calcium chloride at an effective dose may be considered as an alternative to surgical castration.