An oil implicated in the Spanish "toxic syndrome" was studied for its effect on fat digestibility and adipose-tissue composition in rats. The effects produced by the mixture of oils and those induced by the presence of oleoanilides were assessed separately. For 4 wk, Wistar rats were fed diets containing either a mixture of oils similar to that constituting the toxic oil, the same mixture of oils supplemented with oleoanilides, or the toxic oil (which also contained oleoanilides) and were then compared with a group fed olive oil. Food consumption fluctuated sharply in the group fed the toxic oil, falling significantly in the last week of the study. The digestibility coefficient of the various fats was similar, although the rats fed the toxic oil did absorb less fat because of the lower intake. The nitrogen content of the periovarian adipose tissue was highest in the rats fed the toxic oil, and the adipose-tissue fatty acids most affected by this treatment were linoleic and linolenic acid. The delta-9 desaturase activity, measured in terms of the C16:1/C16:0 and C18:1/C18:0 ratios, was significantly less in the group fed the toxic oil, which suggests functional modifications of the adipocyte related to lipogenesis.