Although it is well established that the formation of eicosanoids by ovine intrauterine tissues increases during pregnancy and at the time of labour, the biochemical mechanisms involved remain to be clearly established. In this study, we tested the hypothesis that the gestational and labour-associated increases in eicosanoid formation are associated with a reduction in the activity of the reacylating enzyme, acyl Coenzyme A lysophosphatide acyltransferase (LAT). To evaluate this proposal, in vitro LAT activity was quantified in ovine placenta (cotyledons) obtained during pregnancy (85–147 days of gestation and at the time of labour). Ovine placental LAT increased from 1·81 ± 0·06 nmol/min per mg protein at 85 days of gestation to 2·34 ± 0·10 nmol/min per mg protein at 142 days of gestation (P<0·005, n=15). The apparent Km did not vary significantly between the 85- and 142-day groups. Vmax, however, was significantly greater in the late-gestation group (2·98 ± 0·02 nmol/min per mg protein) than in the mid-gestation group (2·38 ± 0·13 nmol/min per mg protein, P<0·05). In association with labour, placental LAT activity decreased by 16% (1·96 ± 0·13 nmol/min per mg protein) when compared with that observed in tissue obtained from the non-labouring ewe (P<0·01). The data obtained are consistent with the hypothesis that changes in LAT activity in ovine placenta do not contribute to the gestational increase in prostaglandin formation, but a contribution to the labour-associated increase in non-esterified arachidonic acid availability and eicosanoid formation cannot be negated.