To study the effects of dietary trilinoelaidate (tt18:2) on metabolic parameters, as they relate to essential fatty acid metabolism, a diet containing "adequate" linoleic acid with incremental isocaloric ttl8:2 supplementation was formulated. This diet was fed to rats for 11 weeks and oxygen (O2) consumption, insensible water loss (IWL), growth parameters and liver fatty acid composition evaluated at specified time intervals. The results showed that while an essential fatty acid deficient diet (hydrogenated tallow) increased IWL and decreased body weight gains, O2 consumption remained unaltered. Dietary tt18:2, while accumulating in liver lipids, apparently inhibiting delta 6 desaturase, as evidenced by 18.2/20.4 ratios, did not alter O2 consumption of IWL. At the highest level of tt18:2 fed (2.5 weight percent of dietary fat) there was a noticeable decrease in body weight gains by the 11th week; organ weights, however, were not affected. While the increased consumption of dietary trans fatty acids has raised questions regarding their potential biologically detrimental effects, the present study indicated that gross metabolic alterations related to classical essential fatty acid deficiency symptoms are not precipitated in the rat by tt18:2 levels comparable to those consumed in a normal human diet.