The Division of Cancer Prevention and Control, National Cancer Institute (NCI) is conducting a study to evaluate the effect of a fat-modified diet on hormones during childhood and adolescence. The study is being performed ancillary to the Diet Intervention Study in Children (DISC), a randomized clinical trial sponsored by the Division of Epidemiology and Clinical Applications, National Heart, Lung, and Blood Institute (NHLBI). The objectives of DISC are to determine whether a fat-modified diet in childhood and adolescence will lower LDL-cholesterol and to assess the feasibility and safety of this diet. The objectives of the NCI ancillary study are to evaluate the effect of this fat-modified diet on sex hormones and to correlate characteristics of children and adolescents, such as age, Tanner stage, anthropometry, diet, and physical activity, with hormone levels. DISC is being conducted at six clinical centers and a coordinating center under a cooperative agreement with NHLBI. A total of 663 children were randomized into the trial beginning in 1986 and it is anticipated that they will be followed through the 2000. The NCI ancillary study on hormones was initiated in 1991. NCI's contract with Ogden BioServices Corporation is to serve as the DISC hormone laboratory. Ogden will store serum collected for the ancillary study, subcontract with a laboratory to assay hormones in serum, develop and implement an external quality control program, and monitor laboratory performance. The contract with Ogden was awarded for the period September 1993 through February 2001. The PI at Ogden is Ms. Susan Greenhut.