The effect of experimental infection with the intestinal trematode, Echinostoma caproni, on feed intake, liveweight and serum pregnancy-associated murine protein-1 (PAMP-1) and corticosterone was investigated in non-pregnant female BALB/c and Swiss T.O. mice. Twenty-five metacercariae were given by oral gavage on day 0 of which 19.6 % were recovered at post mortem on day 46 in the BALB/c mice and 22.0 % in the Swiss T. O. mice. Oral praziquantel treatment (50 mg/kg) on day 39 reduced the recovery of flukes from previously-infected mice by 85.4% and 100% in BALB/c and Swiss T.O. mice, respectively. The food consumption in the infected Swiss T.O. mice was significantly increased compared to the infected-treated and the controls. In the BALB/c mice the food intake in the infected and infected-treated animals was significantly increased compared with the controls. The liveweight gain during the experiment in the BALB/c control mice was significantly higher than in the infected-treated groups. In the Swiss T.O. mice the infected animals gained more weight than the controls and the infected-treated animals. E. caproni was associated with a significant reduction in PAMP-1 concentrations in both strains of mice, even in animals from which the majority of flukes had been removed by praziquantel-treatment. There was no significant correlation between the magnitude of the parasite burden and serum PAMP-1 values. Corticosterone values were unaffected by either mouse strain, E. caproni infection or anthelmintic treatment. These results suggest that the previously reported adverse effect of. E. caproni on early pregnancy in mice may be caused by parasite-induced effects occurring prior to fertilisation.