A randomized placebo-controlled study was made of the clinical efficacy of four different methods of intravascular laser blood irradiation (ILBI) with helium-neon laser in 150 patients suffering from rheumatoid arthritis (RA). As to ILBI methods used, the most remarkable clinical effect was produced by daily procedures. The positive effect of ILBI was of liminal character bearing in mind the power range examined whereas the negative effect of irradiation was dose-dependent. ILBI may cause an exacerbation of the inflammatory process in RA whatever the single dose and frequency of procedures. The best clinical effect with daily ILBI was attained in women, individuals with the presence of rheumatoid factor but with low titers thereof, and in patients with initial stages of RA and minimum inflammation activity. The efficacy of ILBI may be predicted on the basis of the patient's clinical findings.