The aim of this study was to evaluate the hypothesis that the intravulvar injection of a PGF2alpha analogue at weaning just prior to insemination may minimise the effects of summer infertility in pigs. From July to September 1999, two groups of 30 sows were randomly formed each month. The experimental group comprised sows receiving 37.5 microg of a PGF2alpha analogue, D-cloprostenol, in 0.5 ml injected into the vulvar lips at weaning and at insemination. Group 2 sows received 0.5 ml of saline solution injected into the vulvar lips and served as controls. The percentage of sows in oestrus within 7 days after weaning in treated sows was 27.93% higher than in controls (P<0.001). Fertility for treated sows was also significantly increased by the treatment (P<0.01). However, neither the percentage of inseminated sows that farrowed nor litter size was affected by treatment.