The productivity of the pig ranks high when compared with other classes of farm mammals. Reproductive potential is the most important factor contributing to total meat production from the species, and one which is markedly influenced by husbandry practice. Although many consider the pig not to be a seasonal breeder due mainly to its many years of domestication, it has recently become apparent from several overseas reports that this may not be so, a reduction in fertility having been noted to occur during the hot season of the year. A lack of comparable data for New Zealand conditions, where the recent movement of the industry towards larger and more intensive enterprises has created the need for more efficent production, stimulated the conduct of this study. It was undertaken with the objective of determininq whether a seasonal trend in pig production existed in New Zealand, and if so, likely causal factors of the variation. The study comprised an analysis of records collected over a seven year period in one herd.