Intramuscular injections (10mg) of prostaglandin F2ä were administered to 19 pregnant sows in one herd on either the 112th or 113th day of gestation and a similar number of untreated sows served as controls. Induced sows for up to 6h after injection generally showed/more walking, drinking defaceating and postural changes. Over the last 20h prepartum they spent more time lying and urinated more frequently. Mean interval from injection to onset of parturition in treated sows was 24.5h and 16 of them commenced farrowing during the working day, compared with 6 in the control group. Induction of parturition did not influence litter size at birth, piglet bodyweights at birth or 14 days of age, the incidence of the mastitis, metrititis agalactae syndrome, re-breeding interval of the sow or size of the subsequent litter at birth. Farrowing time was significantly longer (6.48h v 4.08h) for treated sows and litter pre-weaning mortality was higher but not significantly so. Most piglet deaths in each group resulted from overlaying or starvation but mortality from anaemia and septicaemia occurred only in the treated group. It is considered that the technique could have practical application on well-managed intensive pig units.