Collagen type II‐spedfic long‐term cultured T helper cells, derived from the DBA/1 mouse, have been established and characterized. Clones from these T‐cell lines could he shown to recognize either species‐specific or species‐nonspecific determinants on the collagen type II molecule, including determinants on autologous mouse collagen. Induction of arthritis via transfer to both irradiated and normal syngeneic recipient mice was obtained with both collagen type II‐specific T‐cell lines and an autoreactive and collagen type II‐specific T‐cell clone. Fewer cells were needed to evoke arthritis in normal than in irradiated recipients. Cells from lines and the clone used for transfer were by immunocytochemistry shown to have T helper phenotype.