Abstract MEINECKE (1968) and Hoffman and Gingrich (1968) found that the organism Bacillus thuringiensis, Berliner or its spores possessed considerable potential for the biological control of poultry lice. To the authors’ knowledge the potential efficacy of preparations of Bacillus thuringiensis, Berliner for control of poultry mites has not been reported. The occurrence of a red mite (Dermanyssus gallinae) infestation of laying hens at the Poultry Research Center, North Dakota State University afforded an opportunity to evaluate Biotrol® BTB-183 2 (a preparaton of Bacillus thuringiensis, Berliner) alone and in combination with Savol® 3 (a paraffin-based liquid which enhances dispersion of wettable powders) for treatment and control of this parasite. MATERIALS AND METHODS White Leghorn hens kept in stair-step design wire-cages were used. Each cage contained two hens and a continuous set of ten cages comprised an experimental unit. Each mite treatment was applied to two units located adjacent to each other, one being on. . .