Anecdotal reports suggest that abortion occurs in New Zealand cattle after ingestion of macrocarpa (Cupressus macrocarpa). The clinical signs observed are similar to those seen in abortions caused by ponderosa pine (Pinus ponderosa Laws). Isocupressic acid has been identified as an abortifacient component of the needles of ponderosa pine. Macrocarpa collected from the Palmerston North area contained 0.89% and 1.24% isocupressic acid, compared to 1.70% isocupressic acid in Ponderosa pine needles from Oregon in the United States as analysed by the USDA-ARS Poisonous Plant Research Laboratory. These findings support observations that macrocarpa causes abortion in late gestation cattle in New Zealand and suggest the causal agent is probably isocupressic acid.