At Imperial College Healthcare NHS Trust in West London we are interested in finding out the effects of hormones that control reproduction and metabolism. We are looking for preferably healthy men (who do not smoke and who are not taking any medication) aged between 18 and 40 years. Volunteers should have BMIs between 18.5 and 25. The studies involve an initial unpaid screening appointment followed by up to 6 study visits at the hospital. People who participate will be paid expenses of up to £150 for each study visit. Please quote Repro Met Study when you respond to this advert.