Interleukin (IL)-2 production by primary DO11·10 T cells in response to L1210 subclones. Tumorigenic clone 3-3, tumour-forming subclones 7-23 and 7-41, and immunogenic clone 7-15·6 were pulsed overnight with whole ovalbumin (OVA) or ovalbumin peptide (pOVA) and then combined with primary DO11·10 T cells for 24 hr at different effector-to-target (E:T) ratios. Supernatants were collected and assayed for IL-2 by enzyme-linked immunosorbent assay (ELISA). Bars represent the means (± standard deviation) for triplicate wells and each graph shown is one representative experiment of four independent experiments performed; (a) 5 μm OVA; (b) 0·2 μm pOVA. *, P< 0·01, compared with L1210 tumour-forming subclones. PMA/I, phorbol 12-myristate 13-acetate and ionomycin.