These guidelines are intended to help those who design and conduct investigations of psychopharmacologic agents in children. A progression of studies in four phases is advocated. First, early short term studies should establish single and multiple dose safety baselines. Second, early pilot efficacy studies may be initiated jointly with longer duration safety studies. Third, doubleblind placebo-controlled studies should be performed on small, homogeneous groups of subjects to establish objective evidence of efficacy. Finally, controlled clinical trials should be conducted in a variety of clinical settings selected to reflect the ultimate use of the drug. Long term follow up studies should also be initiated at this stage. Each phase of testing is discussed in detail. Eleven appendices intended to amplify procedures and measures discussed more generally in the guidelines are included. Appended materials discuss general principles, clinical evaluation, diagnostic classifications, behavior observations and activity measures, performance tests, global rating scales, preschool behavior rating scales, self report measures, social and emotional assessment, environmental assessment, and assessment of side effects of drugs in children. (Author/RH)