The most important method for evaluating the pathogenesis of male infertility is open testicular biopsy. Herein we describe a method of aspiration biopsy of testis for histologic examination. Sexually mature dogs and rats treated with chemotherapeutic agents and ionizing radiation were followed with periodic testicular aspiration biopsy during and after treatment. The histologic findings from the aspiration biopsy compare with the results of routine histologic examinations in assessing spermatogenetic activity and delineating pathologic changes. The puncture in the experimental animals was performed under general anesthesia. In human patients testicular biopsy could be done under local anesthesia in an outpatient clinic. The procedure would be less painful, minimally invasive, and more cost-effective.