Sera from 12/1,155 (1%) anti-HCV-negative (Elisa) UK blood donors were found to be anti-GOR positive. None out of 12 of those sera were positive for HCV RNA by the reverse transcriptase/polymerase chain reaction (RT/PCR). In a cohort of 316 anti-HCV Elisa-positive sera, 27/57 RIBA-positive, and 1/188 RIBA-negative sera were anti-GOR positive, resulting in a sensitivity of 47% and a specificity of 99.5% for anti-GOR as a marker for RIBA-confirmed HCV infection. Four out of 71 (6%) of RIBA-indeterminate sera were anti-GOR positive. Donors with anti-GOR reactivity were more likely to have antibodies against each of the individual HCV antigens represented in the RIBA, and those antibodies were of greater intensity, when compared to the anti-GOR negative cohort. Twenty out of 36 (55.6%) of RT/PCR-positive sera were anti-GOR positive, compared to 1/7 (14.3%) of RT/PCR-negative sera (p = 0.09). The usefulness of anti-GOR testing of UK blood donors is discussed in the light of these results.