Blood samples taken from the ear vein of 1037 sows two to three weeks after service were assayed the same day using Ovucheck 'Sowside' kits. Colour development was compared with oestrous and pregnancy controls. Reliable data on reproductive performance were obtained from 908 sows sampled 17 to 20 days after service. The accuracy of identification of 796 pregnant and 12 non-pregnant sows was 94.6 per cent and 35.7 per cent, respectively. Excluding animals which returned outside the normal range of 18 to 24 days, 52.1 per cent of 48 empty sows were identified by the test. Problems with blood sampling were reported on seven of 18 farms and this may explain the low accuracy of the kit on some farms.