Luteinizing hormone (LH) is an important hormone of the reproductive system, which has found application in diagnosis and therapeutic medicine. It plays a vital role in the development and functioning of the reproductive system. Determination of LH concentration is important for detection of dysfunction of the pituitary-ovarian axis, diagnosis of reproductive disorders, monitoring of antifertility programmes and in therapeutic preparations. On the basis of heterogeneity and various biological effects served by the hormone, different assay systems have been developed for its estimation. Initially, LH was quantified on the basis of in vivo and in vitro endocrine activity. However, with the advancement in biotechnology, various immunoassays have been designed for performing most of the physiological and clinical studies on serum LH. The immunoassays offer improvement in sensitivity, precision and convenience over bioassays. However, these immunoassays have their own limitations and results obtained in different laboratories are often not comparable. This review makes an attempt to enumerate and compare various assay methods used in the serum LH measurement in varied clinical conditions.