Using a monochromator, 10 patients with atopic dermatitis were treated with 300 +/- 5 nm rays (UVB) and with 350 +/- 32 nm (UVAB) rays to compare the efficacy of these 2 wavebands. In each patient, 2 well-defined dermatitis patches were irradiated with 1 of the 2 wavelengths 5 d per week for 2 weeks. Each patch was subject to evaluation on 7 effect variables, the sum of which comprised the total score. The effect of these wavelengths on the 2 variables considered to be of greatest importance was subjected to statistical analysis. The UVAB light proved to be superior to the UVB light for both total score and overall evaluation score.