Low-fat conventional diets supplemented with 5 or 10% vegetable oils were fed to stroke-prone spontaneously hypertensive rats (SHR-SP) from weaning and the mean survival times were determined. A 1% aqueous sodium chloride solution was used as drinking water throughout the experiments. In four separate experiments, the rapeseed oil group showed a significantly shorter mean survival time. The relative mean survival times were 50-59% (rapeseed oil group), 78-100% (soybean oil group) and 86% (microbial oil group) as compared with the group fed perilla oil (100%). The group which received 4-fold diluted rapeseed oil exhibited a significantly shorter survival time as compared with the group receiving soybean oil. Although the feeding experiments were performed under very simple and restricted conditions, these results suggest that the rapeseed oil prepared for human use contains a factor (s) which is toxic to SHR-SP rats.