We have previously shown an increase in nerve growth factor (NGF) levels and in mast cell (MC) distribution in the synovium of patients affected by rheumatoid arthritis. We now report that purified NGF antibodies injected into arthritic transgenic mice carrying the human tumour necrosis factor-alpha (TNF-alpha) gene caused reduction in the number of MCs, as well as a decrease in histamine and substance P levels within the synovium. These observations suggest that NGF antibody might be useful in studying the role of these pro-inflammatory markers in joint arthritis.