Technical Abstract: Dairy Herd Improvement data on 325,722 cows from 35 states were used to examine the relationship of test-day somatic cell score (SCS) with measures of fertility in US Holsteins and Jerseys. In addition, other factors such as herd, year, month, parity, stage of lactation, and calving ease score were examined to determine their influence on days to first breeding, days open, and 70 day non-return rate to first service (NRR), and ensure that the effect of SCS was estimated independent of other effects. Non-return rate was highest in April and May and lowest in June. Parity had a large effect on NRR and was 6 to 7% higher in first than in sixth and later parities. Effect of stage of lactation at first service was large, with NRR rising 9-10% from early to late lactation. Calving ease score had a significant effect on NRR,with a decline of 6 to 7% from score 1 to score 5. In Holsteins,significant but small linear regressions were found for non-return rate on preceding test-day SCS. This relationship was not significant in Jerseys. The magnitude of the effects do not warrant postponing breeding when SCS is high.