Abstract : In 2/3 of infertility problems, the male partner is, partially or entirely, responsible. His investigation starts with a careful history and is followed by a thorough physical examination. Then, comes the spermogram. In addition to an assessment of the number, motility, and morphology of spermatozoids, this examination must involve a spermocytogram, tests of anti-spermatozoid immunity, and a bacteriological analysis. The biological study of the seminal plasma is also of considerable value. Electron microscopy of sperm is valuable in asthenospermic men. A genetic and hormonal investigation is, nowadays, almost mandatory in all cases. Testicular biopsy with cryopreservation of testicular tissue and demonstration of a possible varicocele can also, in selected cases, be of great help. The overall strategy will be decided on the basis of the whole investigation