A case-control study of clinical, endocrine and seminal characteristics in 86 infertile men and a prospective study of conception rates during 804 follow-up cycles among 75 infertile couples with male immune infertility were performed. Genito-urethral infections or surgery, and palpable epididymal abnormalities were more common among the immunological cases than among the non-immunological infertile controls (n = 180), but sperm concentration, motility and morphology were similar. The spontaneous conception rate in 70 cases was 1.7% per cycle. Treatment by intra-uterine insemination (IUI) resulted in 8.6% pregnancies per cycle, conventional in vitro fertilization (IVF) had a 18.4% success rate per attempt, and two out of three couples treated by intracytoplasmic sperm injection (ICSI) attained pregnancy. Minimal sperm quality required for successful IUI was not lower than that recorded in couples with spontaneous conception. It is concluded that immunological infertility, as diagnosed by a positive mixed antiglobulin reaction (MAR) test, is associated with a low spontaneous conception rate. Techniques of assisted reproduction are useful in the management of couples with infertility resulting from this pathology, but sperm characteristics required for successful IUI are much higher than those needed for successful IVF. A strategy for the logical management of this pathology is proposed.