Five micrograms of human β-tryptase was injected into the knee joint cavity of two groups of anaesthetized (Halothane/O2/N2O) mice (30 g): wild-type (PAR-2+/+) C57BL/6J mice and PAR-2 gene disrupted mice (PAR-2-/-). Joint swelling was assessed by comparing caliper measurements of knee joint diameter pre-injection and post-injection. Chronic monoarthritis was induced using the same anaesthetic regime in separate wild-type mice by intra-articular and peri-articular injection of Freunds complete adjuvant (FCA) (in 5% methycellulose). In a parallel group of mice, 50 μg of the tryptase inhibitor 4-amidino phenyl pyruvic acid (APPA) was co-administered with the FCA/methycellulose emulsion. Joint diameter was measured over 10 days.