A variety of mutations and polymorphisms of genes regulating female and male reproductive functions have been discovered during the last few years. These include several inactivating and activating mutations in LH receptor genes. The first mutation of FSH receptor (FSHR) gene was discovered in six Finnish families. This inactivating Ala189Val transition in the extracellular receptor domain causes primary amenorrhea, arrest of follicular development and infertility in homozygous women. In contrast to females, this mutation did not cause absolute infertility in males but only suppressed spermatogenesis. Another inactivating mutation of the FSHR gene has been found at position 191 (Asn191Ile) in a healthy fertile woman. The studies on inactivating FSHR mutations demonstrate that normal ovarian function is critically dependent on FSH while, in contrast to earlier views, male fertility is less strictly dependent on normal FSH action.