A case-control study of the management and disease risk factors associated with toxic mastitis in cows was carried out. Seventy-one cases satisfied all the selection criteria, and a subset of 41 cases in which pure growths of Escherichia coli were cultured from milk samples was also investigated. Conditional multiple logistic regression analysis of the 71 cases and matched controls revealed no statistically significant associations. However, among the subset of 41 cases and matched controls, the administration of calcium parenterally at calving (P<O.O1) and assistance at calving (P<O.O1) were both associated with toxic mastitis. Controlling for assistance at calving, the odds of a cow developing E coli toxic mastitis if it had received calcium parenterally at calving were 23 times higher than for a cow that had not received calcium. Similarly, controlling for the administration of calcium at calving, the odds of a cow developing E coli toxic mastitis if it had received assistance at calving were 11 times higher than for a cow that did not receive assistance.