The effects of 50% ethanol extract of Martynia annua L. root on reproduction was studied on male rats. The study was divided into four groups of five animals each. The first group (I) received vehicle alone to serve as control. The second, third and fourth groups (II, III and IV) of animals were administered the root extract daily at 50 mg/kg body weight, po, 100 mg/kg body weight, po, and 200 mg/kg body weight, po, respectively, for a period of 60 days. Significant decreases in the weights of testes, epididymides, seminal vesicle and ventral prostate were observed. A dose related reduction in the testicular sperm count, epididymal sperm count and motility, number of fertile males, ratio between delivered and inseminated females and number of pups were observed. The testis showed a clear correlation between the dose and severity of lesions of seminiferous epithelium. In general, the seminiferous tubules appear reduced in size with a frequently filled eosinophilic material. Spermatogenesis arrested at the secondary spermatocyte stage. Pachytene spermatocytes were undergoing degeneration. Disorganisation and sloughing of immature germ cells were visible. Leydig cells were atrophied. No morphological changes were observed in Sertoli cells. Significant reduction in serum concentration of luteinising hormone and testosterone were observed. No distinct change in serum FSII concentration was recorded. The final body weights of all groups were elevated markedly. No alterations were recorded in any hematological parameters. It is concluded that the 50% ethanol extract of M. annua root produced dose related effects on male reproduction without altering general body metabolism.