Percentage arterial oxygen saturation (SpO2) was measured in 69 neonatal lambs at one, five and 10 minutes after birth using a pulse oximeter applied to the tail. The lambs were given a subjective vitality score from 1 to 4, with 1 being normal and 4 being stillborn. Of the 42 lambs born after a normal parturition, 19 were measured after one minute, 29 after five minutes and 24 after 10 minutes; the mean (sd) SpO2 values of these groups were 67 (15) per cent, 84 (9) per cent and 83 (9) per cent, respectively. Of the 27 lambs born after dystocia, 16 were measured after one minute, 18 after five minutes and 12 after 10 minutes; the mean (sd) SpO2 values of these groups were 61 (15) per cent, 69 (16) per cent and 69 (19) per cent, respectively. The values measured in the lambs born after dystocia were significantly lower than those in the lambs born normally at five and 10 minutes (P < 0.005 and P < 0.05, respectively). Of the lambs born with a vitality score of 1, 24 were measured after one minute, 33 after five minutes and 26 after 10 minutes; they had mean SpO2 values of 72 (11), 82 (10) and 81 (12) per cent, respectively. Of the lambs born with vitality scores of 2 or 3, 11 were measured after one minute, 14 after five minutes and 10 after 10 minutes; they had mean SpO2 values of 48 (6), 68 (17) and 72 (20) per cent, respectively. The SpO2 values of the lambs with vitality scores of 2 or 3 were significantly lower than those of the lambs with a vitality score of 1 at one and five minutes after birth (P < 0.0001 and P < 0.05, respectively).