A commonly available aerosolized pyrethroid insecticide containing deltamethrin and imiprothrin is widely used for hygienic control in Egypt. The immunotoxic effects after inhalation exposures to the preparation of each for 2, 10, and 30 days were investigated in rats. For each exposure, the insecticide (containing 0.2% imiprothrin and 2.5% deltamethrin) was sprayed in all directions in a room (using a special attachment located in the ceiling in the center of the room) for 30 s each minute for 15 min; the room was then kept closed for 15 min. After each spray interval, the rats were introduced for 30 min and then removed to a clean room. The exposure process was repeated a total of three times on each day of the respective regimens. The interval between the 15-min spray/15-min pause/30-min rat exposure cycles was 120 min. Twenty-four hours after the final exposure in each particular regimen, the cohort rats in the regimen (air and exposed) were weighed, sacrificed, and their tissues were removed for analyses. Immunological tests performed included assessments of potential changes in immunopathology (determined from body and splenic weights), humoral-mediated immunity (based on plaque-forming activity of spleen cells), cell-mediated immunity (determined from splenic lymphocyte responsiveness to stimulation with phytohemagglutinin and immune cell (sub)type profile analyses), and nonspecific immunity (based on phagocytic activity of peritoneal macrophages). The results indicated that of all the endpoints examined, among the rats exposed over a 2-day period to the imiprothrin- and deltamethrin-containing insecticide aerosol, the only significant change noted (relative to values from time-matched controls) was in the levels of splenic CD4+CD8- and CD4+ CD8+ cells. In contrast, exposures on each day of a 10-day period led to significant decreases in several endpoints; exceptions to this were values for body and spleen weight (unaffected), splenic OX12-OX19+ levels (significant increase), and CD4+CD8- levels (unaffected, relative to control). Rats exposed for 30 days displayed significant decreases in each test applied, except for increases in both splenic OX12-OX19+ and CD4+CD8- cell levels relative to corresponding control rat values. The present study findings indicate that repeated noncontinuous inhalation of a commonly utilized insecticide that contains imiprothrin and deltamethrin can cause a variety of immunotoxic effects in sites distal to the lungs.