20 patients with active rheumatoid arthritis were treated for 12 weeks with the prostaglandin E, precursors cis-linoleic acid andγ-linolenic acid in the form of primrose evening oil (Efamol®) and the co-factors zinc, ascorbic acid, niacin, and pyridoxin (Efavit®). There was a slight fall in skin reactivity to UV light during the treatment, but no effect on plasma or urine concentrations of PGE1, cAMP or cGMP. There was no effect of the treatment on ESR, P-fibrinogen, number of tender joints, number of swollen joints, the duration of morning stiffness, or on the patient's estimation of pain.