In a field trial the effect of a commercial preparation containing 400 IU PMSG/200 IU HCG per dose (Suigonan vet) was studied in 20 anoestrous gilts and 39 anoestrous sows. Immediately before the hormone treatment blood samples were taken for determination of the plasma progesterone level. The correlation between the pretreatment plasma level of progesterone and the response to the hormone treatment was analysed. The mean number of litters per sow at treatment was 3.0 and the mean lactation period 38 days. The mean period from weaning until treatment was 21 days. The average age of the gilts at treatment was 263 days. In 38.5% of the sows and 35% of the gilts the plasma progesterone level was greater than 3 nmol/l, indicating that these animals had corpora lutea in the ovaries. In the sows a total of 79.5% showed oestrus, but only 56.4% within 7 days after treatment. The mean progesterone level for the sows showing oestrus within 7 days was low, 1.5 nmol/l. Sows showing oestrus more than 7 days after treatment (23.1%; mean 18 days) or not showing oestrus (20.5%) had a high mean progesterone level of 48.9 nmol/l and 23.6 nmol/l at treatment, respectively. A total of 75% of the gilts showed oestrus, 60% within 7 days after treatment, the latter with a mean plasma progesterone level of 2.4 nmol/l at treatment. Fifteen per cent showed oestrus more than 7 days after treatment (mean 32.3 days) and in 25% no oestrus was observed.(ABSTRACT TRUNCATED AT 250 WORDS)