A study was made of calving rate resulting from 2876 exposures to mating of Zebu cattle grazing cleared jungle land in the Amazon basin, Peru. Calving rate were calculated for each mating opportunity. The overall mean rate was 59 per cent, but it was lower (49 per cent) at the second opportunity. The low proportion of cows which calved regularly each year was shown. Calving intervals varied from 464 ± 141 days (third) to 614 ± 157 days (first) in duration. The mean body weight at first mating of heifers which calved at the first opportunity (265 ± 29 kg) exceeded the weight of those which did not calve by 16 kg (P < 0·01). Heifers which calved at both the first and second opportunity weighed 277 ± 33 kg at first mating compared with 262 ± 27 kg for those which calved only the first time (P<0·0l). It was concluded that the calving rate described was too low to cover costs and the ways in which improvement is being sought are mentioned.