Live Lactobacillus paracasi 33 (LP33) may effectively improve the quality of life for patients with perennial allergic rhinitis. It has been demonstrated that heat-killed lactic acid bacteria (LAB) suppress specific immunoglobulin E synthesis and stimulate interleukin-12 production in animals. The aim of this study was, therefore, to evaluate the efficacy of heat-killed LP33 in the treatment of allergic rhinitis induced by house-dust-mite in human subjects. A total of 90 patients were enrolled in a randomized, double blind, placebo-controlled trial and assigned to three treatment groups. Patients in groups A and B received two capsules per day of live or heat-killed LAB (5 x 10(9) colony-forming units/capsule), respectively, over a period of 30 days while those in Group C received placebo capsules. A modified questionnaire on pediatric rhinoconjunctivitis-related quality of life was administered to all subjects or their parents during each clinical visit. The overall quality of life score decreased for groups A and B, as compared with the placebo group, in terms of both frequency (9.47 +/- 2.89, 6.30 +/- 2.19, vs. -3.47 +/- 1.53, respectively; p < 0.0001) and level of bother (5.91 +/- 3.21, 6.04 +/- 2.44, vs. -2.80 +/- 1.64, respectively; p = 0.004) after the 30-day treatment. The efficacy of the heat-killed LP33 was not inferior to the live variant. No obvious side effects were reported for either active treatment group during the study period. Our results suggest that heat-killed LP33 can effectively improve the overall quality of life for patients with allergic rhinitis, and that it may be efficacious as an alternative treatment.