The essential fatty acid requirement for the development of intestinal carcinogenesis was determined and compared to the overall essential fatty acid status of the animals as measured by the triene/tetraene ratio in the plasma, liver and colon. To induce tumors, male Sprague-Dawley rats were given two weekly injections (20 mg/kg body wt) of azoxymethane. Two weeks after the last injection, the rats were divided into groups of 25 and given one of six diets containing various levels of essential fatty acids (as linoleate). The diets contained 5% total fat and were prepared by mixing safflower oil (high essential fatty acids, beef fat (low essential fatty acids), and medium chain triglyceride oil (no essential fatty acids). One group of rats was fed a 20% beef fat diet. The range of essential fatty acids was from less than 0.03% to 1.28% (w/w). Twenty-six weeks after the first azoxymethane injection, the animals were killed and intestinal tumor incidence and multiplicity were determined. Samples of plasma, liver and colon were also taken for measurement of the triene/tetraene ratio by gas chromatography. Large bowel tumor incidence showed a dependence on the essential fatty acid content of the diet. The results were as follows: (percent essential fatty acids: percent tumor incidence) Group A (1.28: 72.4), Group B (0.60: 73.3), Group C (0.11: 55.2), Group D (0.08: 39.3), Group E (less than 0.03: 37.9) and Group F, which was fed 20% beef fat, (0.34: 88.5).(ABSTRACT TRUNCATED AT 250 WORDS)