The study aims to elucidate the role of leptin in the regulation of human endocrine function approached by a carefully designed, prospective clinical study of the rapidly-sampled dynamics of endocrine rhythms during the course of leptin-replacement treatment in the only three adult individuals identified in the world so far who are leptin-naive due to a functional leptin gene mutation. A study of leptin-naive subjects avoids all confounding factors and pitfalls, because the only bioactive leptin to which they will be exposed is the exogenously administered recombinant protein. Thus, this proposal will permit us to ascertain the endocrine effects of human leptin.