The ability of microbial agents in organic dust to attract alveolar macrophages (AM) and neutrophils (PMN), and to stimulate the release of chemotactic factors by AM was studied. The cytotoxicity of Enterobacter-agglomerans extract or endotoxin, Thermoactinomyces- vulgaris extract, thermophylic bacterial protease, Aspergillus- fumigatus extract, Baker's yeast glucan, and barley glucan were determined by incubation with AM from English-short-hair-guinea- pigs. Significant toxicities were noted at 1,000 micrograms/milliliter (microg/ml) for all but barley glucan. Concentrations of 0.1 to 10.0microg/ml were selected for chemotactic assays. Chemotactic effects of agents on guinea-pig AM and human PMN were measured using a blind well chemotaxis chamber technique. All agents attracted significantly more AM and PMN than the control buffer solution. Baker's yeast glucan and E-agglomerans extract and endotoxin had significantly higher attraction abilities for AM than the other agents. The least active in attracting AM were Barley glucan and T-vulgaris extract. Barley glucan and E-agglomerans extract and endotoxin were significantly more attractive to PMN than the other agents. The least active in attracting PMN were A- fumigatus extract and protease. Using supernatant from agent exposed AM, the ability to stimulate AM release of chemotactic factors for other AM and PMN was determined. The released chemotactic factors were even more potent attractors of AM than the agents themselves. Baker's yeast glucan, protease and A-fumigatus extract induced the strongest response. Released chemotactic stimulators for PMN were induced by all agents. A dose response relationship was observed between concentration of agent and cells attracted for both AM and PMN. The authors conclude that chemotactic activity by AM and PMN is induced by microbial agents found in organic dusts. The authors suggest that such activity by organic dusts in the workplace may play a role in the inflammatory reactions of occupational lung diseases.