The first step is to phone up the clinical centers in your area and ask if they need healthy volunteers for upcoming studies. To find the clinics that conduct these studies, a good directory is essential, as relatively few studies are advertised. Conveniently, BioTrax has the most comprehensive and informative directory available today. And our data-base provides contact information for over 500 clinics and consumer study houses in 23 countries, probably the majority in existence world-wide. When you phone a clinic, you will usually be asked a number of questions in order to determine your eligibility to screen for the study. These questions will concern your medical history as well as your lifestyle habits, which include your diet, level of physical activity, and what intoxicants, stimulants and other substances you partake of, and how much. If you answer the questions correctly, you will then be invited to screen for a study. You may be given a choice of studies, and informed as to the length and dates of each. Most clinics will tell you what the study pays, but some wait until you have completed the screening.