A trial was conducted to examine the effect of polarized light on pressure ulcers of 1st, 2nd and 3rd grades. Patients with two pressure ulcers, one of which received the polarized light therapy (experimental ulcer) and the other acting as control, were included in the study. The experimental ulcers received treatments for 2 weeks consisting a 5 min therapy session each day, excluding weekends, for 10 days. Experimental and control ulcers were assessed as they appeared on admission and reassessed at the end of each week. Fifty-five patients aged 37-85 years (67.1 +/- 11.9 years) were studied. Pressure ulcers of 1st, 2nd and 3rd grades receiving extra treatment with polarized light had increased values of epithelial tissue between the first and second assessments of 0-30.9% and between the second and third assessments of 30.9-21.7%. Values of the control pressure ulcers were, respectively, from 0 to 5.5% and from 5.5% to 3.1%. The mean pink/white colour values of the experimental ulcers, between the first and second measurements increased significantly compared with the control ulcers (P = 0.021) and also increased significantly between the second and third measurements (P = 0.003). The mean values of 'no and minimal exudate' of the experimental ulcers increased significantly between first and second measurements compared with the control ulcers (P = 0.001), and similarly, significantly between the second and third measurements (P = 0.002). Mean surface areas of the experimental ulcers decreased significantly between the first and second measurements from 2.84 to 2.54 cm2 (P < or = 0.001) and between the first and third measurements from 2.84 to 2.26 cm2 (P < or = 0.001). Mean surface areas of the control ulcers decreased between the first and second measurements from 2.10 to 2.08 cm2 (P < or = 0.42) and between the first and third measurements from 2.10 to 2.04 cm2 (P < or = 0.007). Pressure ulcers subjected to extra treatment with polarized light in the early stages (first to third measurements) showed improvement in the healing process than the control ulcers.