TCA3 is a cDNA originally isolated from activated T cells. Transcription of this gene has been shown to correlate with Ag-induced cellular activation of both T cells and mast cells. Based on the predicted amino acid sequence encoded by the cDNA, we previously proposed that TCA3 represents a cytokine. In this report we have used rDNA technology to express TCA3 in two mammalian cell lines. In both cases, TCA3 was expressed as a secreted molecule with an apparent molecular mass of 16 kDa. Digestion of the (rTCA3) with the enzyme N-glycanase revealed that approximately 8 kDa is caused by N-linked glycosylation. Intradermal injection of rTCA3 into mouse footpads resulted in a rapid swelling response. The sites of injection were characterized histologically by a local accumulation of neutrophils. These findings are discussed with particular attention to a family of related proteins, some of whose members also have inflammatory properties.