Approximately one third of the Norwegian blood donor population has been tested for infection with human T-lymphotropic virus type I and II (HTLV-I/II). This study was initiated to provide an indication as to whether or not the Norwegian transfusion service should screen the entire donor population for HTLV I/II. No HTLV-I infections were found among the blood donors. One new donor was confirmed HTLV-II positive. This individual had previously used drugs intravenously. HTLV-I/II infection can be regarded as a marker for risk behaviour, and testing can be of significance in the quality assurance of the transfusion service. We recommend that the entire blood donor population be tested for HTLV-I/II infections, and thereafter only new donors. The benefit of this scheme should be evaluated in the future.