- ASSESS THE SAFETY OF A DRUG OR DEVICE - take several months to complete - includes a small number of HEALTHY VOLUNTEERS paid for participating in the study (20 TO 100) - DETERMINE THE EFFECTS OF THE DRUG OR DEVICE ON HUMANS including how it is absorbed, metabolized, and excreted (ADME) - investigates the side effects that occur as dosage levels are increased. - 70% OF EXPERIMENTAL DRUGS PASS THIS PHASE OF TESTING - represent the FIRST USE OF THE DRUG IN MAN - Except for certain special situations such as for many cancer and AIDS drugs where no truly safe dose can be anticipated, these studies are performed in normal healthy volunteers. - purpose is to establish a dose-response tolerance relationship, limited by the onset of unacceptable adverse effects.