An experimental canine model was designed to evaluate the effect of granulocyte transfusions on systemic infection with Candida albicans in the granulocytopenic host. Each of a pair of dogs was rendered granulocytopenic with a single intravenous (i.v.) dose of cyclophosphamide (50 mg/kg body weight) and challenged with 10(6) Candida albicans organisms administered i.v. when granulocyte counts were less than or equal to 500/mm3. Granulocytes procured by leukofiltration were infused into six experimental dogs 1, 24, 48, and 72 hr after challenge with Candida. An average of 13 +/- 1.3 X 10(9) granulocytes were administered per infusion, producing an average 1-hr increment of 588 +/- 146 granulocytes/mm3 over the pretransfusion granulocyte count. Experimental and control dogs were killed 96 hr after challenge and organs examined grossly and by quantitative culture techniques to measure the extent of infection. All animals receiving granulocyte transfusions had significantly less tissue infection than nontransfused controls (p less than 0.05). It was concluded that granulocyte transfusions are effective in reducing the severity of infection by Candida albicans during periods of leukopenia.