In 1981, toxic oil syndrome, a progressive multi-system disease caused by consumption of rapeseed oil denatured with aniline occurred in Spain. To date, the causal toxic agent or agents remain unknown. Measures of acidity, moisture, impurities, phosphorous, soaps, and spectrophotometric determinations of color at 409 nm were performed. Since fatty acid anilide concentrations in these oils are associated with risk of disease, w e studied the formation of aniline-derived compounds over time after oil denaturation and by oil deodorization temperatures (200ºC, 215ºC, 230ºC, 245ºC, 260ºC, y 270ºC) and times (3, 4, 4.5, 5, 5.5 and 6 hours). Formation of fatty acid anilide compounds increased with storage time. Deodorization led to a reduction of total anilides in all the samples, particularly at temperatures above 245ºC. Esters of 3-(N-phenylamino)-1,2-propanediol were not detected.