We present a clinical study aimed to compare plasma antioxidant vitamins, vitamin E, beta-carotene and vitamin A. The study consisted of a group (15 patients) with rheumatoid arthritis (RA) compared to a healthy control group. There was a significant decrease in plasma vitamin E, beta-carotene and vitamin A (vitamin E 30.4 +/- 4.9 VS 43.6 +/- 8.2 micrograms/ml, beta-carotene 0.73 +/- 0.26 VS 1.02 +/- 0.22 micrograms/ml and vitamin A 0.22 +/- 0.07 VS 0.46 +/- 0.15 microgram/ml, P < 0.01 patients VS control, respectively). Supplementation of Dunaliella (natural)--beta-carotene to the RA patients for 3 weeks, resulted in a significant increase in plasma vitamin E (47.9 +/- 5.5 micrograms/ml) beta-carotene (0.87 +/- 0.21 microgram/ml) and vitamin A (0.55 +/- 0.15 microgram/ml). There were no changes in the activity indexes of RA. Low plasma antioxidant vitamins in patients with RA are consistent with the observation that oxidative processes occur in the inflammed joints. The validity of antioxidant vitamins as supplementary therapy for RA is not clear.