The effects of various chemotactic factor generation conditions and several chemotherapeutic agents on neutrophil migration were determined using in vitro assay systems designed as models for inflammatory processes occurring in the synovial cavities of patients with rheumatoid arthritis. The microtubule-promoting agent concanavalin A and the microfilament-disrupting agent cytochalasin B were shown in these systems to inhibit neutrophil migration towards zymosan-activated serum-derived chemotactic factors. Neutrophils, immunoglobulin G aggregates, and serum were required for maximum generation of comparable chemotatic factors. Insoluble immunoglobulin G aggregates with or without rheumatoid factor produced more chemotactic factor activity on interaction with neutrophils than soluble immunoglobulin G aggregates. Exposure of neutrophils to supratherapeutic levels of the nonsteroidal antiinflammatory agent aspirin decreased neutrophil response to chemotactic factors while exposure to the slow-acting or immunomodulating agents gold, d-penicillamine, or azathioprine had no effect on this neutrophil function. In vitro systems employing neutrophils, insoluble aggregates, and serum may offer useful means for assaying drug effects on important functional components of the rheumatoid inflammatory process. © 1983 Plenum Publishing Corporation.