The effects of a single oral dose of ethyl linoleate on urinary prostaaglandin E (PGE) excretion and urine output were investigated in essential fatty acid (EFA)-deficient rats. Weanling male rats were fed a fat-free diet. After 13 wk of feeding, eight rats received an oral dose of 400 mg of ethyl oleate. Seven days later the same eight rats received 400 mg of ethyl linoleate. The oleate dosage served as control. Another seven EFA-deficient rats received an oral dose of 100 mg of ethyl linoleate. The 24-hr urine collections from each animal were analyzed for PGE by radioimmunoassay. Within 24 h the oleate dose resulted in a 1.3-fold increase in urinary PGE excretion. The 400-mg dose of ethyl linoleate induced a 2- to 3-fold increase in urinary PGE excretion during 7 d. The 100-mg dose of ethyl linoleate resulted in a 1.3- to 1.5-fold increase for 2 d. Neither the ethyl oleate dose nor the low dose of ethyl linoleate had any effect on urine output, whereas the high dose of ethyl linoleate induced a slow increase during the following 6 d. The present results show that a single dose of 400 mg of ethyl linoleate increased urinary PGE excretion and urine output in EFA-deficient rats. However, these two parameters do not seem to be correlated. The amount of urinary PGE excreted in excess of baseline urinary PGE excretion accounted on a molar basis for less than 1 ppm of the administered dose of ethyl linoleate.