SUMMARYMultinucleated giant cells (MGC) are a common feature of granulomas. The mechanism of their formation has been studied extensively, but their function has not been completely characterized. A new method for the in vivo production of MGC was developed involving subcutaneous injection of microscopic nitrocellulose particles with adsorbed mycobacterial antigens into the footpads of sensitized BALB/c mice (immune [I]-MGC), or by nitrocellulose administration to non-sensitized mice (foreign body [FB]-MGC). The development of granulomas with a highly enriched MGC population was observed 2 weeks after the nitrocellulose injection. MGC were larger with a greater number of nuclei in I-MGC than in FB-MGC. From days 7±28 after nitrocellulose administration, the production of interleukin-1a (IL-1a) and tumour necrosis factor-a (TNF-a) was demonstrated in both MGC types by in situ reverse transcription±polymerase chain reaction (RT±PCR) and immunohistochemistry. After 2 months, the MGC had ceased production of IL-1a and TNF-a, but the expression of transforming growth factor-b (TGF-b) was very high, occurring together with extensive ®brosis. These results suggest that MGC are an active source of in¯ammatory cytokines, which can contribute to the initiation, maintenance and down-regulation of granulomatous in¯ammation induced by immunological and inert substances.