A comparison of this review with the review on the LH/CG receptor that we published in this journal 4 yr ago (1) clearly shows that the field has advanced tremendously in this short period of time. Many of the questions that were unanswered then have now been conclusively answered. On the other hand, as is always the case, the new knowledge generated has also resulted in many new questions that are yet to be answered. Hopefully it is clear from this review that the knowledge and experimental tools generated during the last 4 yr have given us new ammunition to address such important issues as the elucidation of the structural determinants of the LH/CG receptor that are involved in the different functions of this receptor, as well as on the molecular bases of receptor activation, inactivation, and regulation. In fact, since we finished writing this review in September of 1992, we are certain that some of the questions left unanswered here will already have an answer in 1993 when this review is published.