Prophylaxis has been practiced for many years in Europe and is gaining acceptance worldwide with current viral inactivation procedures. Unfortunately, the high cost of praphylaxis is currently the major obstacle to its implementation in developing countries such as Turkey. The aim of this controlled preliminary study is to evaluate the efficacy, safety, and feasibility of prophylaxis. Seven boys aged 1.5-7 years (5.0 +/- 1.8) who had severe hemophilia (six A, one B) received 20-50 IU/kg factor twice weekly and were followed up for 6-24 months (14.5 +/- 6.6). Intermediate concentrates have been used in hemophilia A and ultrapure product for hemophilia B. The data obtained for the same group of patients before prophylaxis were used as a control group. Another control group was selected in another group of IO hemophiliacs, mean age 12.5, and received treatment on demand. During prophylactic treatment, the episodes of bleeding were decreased (from 10.5 +/- 3.2 to 4.5 +/- 3.6). Orthopedic and radiologic joint scores were stable (from 0 to I and from 1.1 +/- 1.2 to 1.0 +/- 1.5). The patients spent significantly fewer days in the hospital (from 18 +/- 12 to 0.7 +/- 0.6). None of the patients was infected with hepatitis A, hepatitis B, or human immunodeficiency virus. One patient was seroconverted with anti-hepatitis C virus in the third month of prophylaxis. Mean consumption of concentrates for prophylaxis was 3489 +/- 960 IU/kg per year compared with 2073 +/- 1302 in conventional therapy. Prophylaxis was superior to treatment on demand even when given in a twice-weekly period with intermediate concentrates. In Third World countries, prophylaxis should be tried at least in selected severely hemophilic children in order to prevent disabilities.