The effect of pre- and post-challenge treatments with trifluoperazine and palmitoylcarnitine, two protein kinase C (PKC) inhibitors characterised by their interaction with the phospholipid enzyme cofactor, on the inflammation caused by delayed hypersensitivity (DTH) to dinitrofluorobenzene (DNFB) and sheep red blood cells (SRBC) in mice is reported. The activity of dexamethasone and two immunosuppressors, azathioprine and methotrexate, is also evaluated. The effectiveness of pre-treatment with each of the test drugs diminished when the DNFB challenge dose increased, whereas trifluoperazine and azathioprine were more active when administered after the challenge at the high DNFB dose. Trifluoperazine, which is also a calmodulin-antagonist, was the more effective of the PKC inhibitors tested on DNFB-DTH (39% and 59% inhibition swelling 24 and 96 h after challenge, respectively). SRBC-DTH was sensitive only to the action of the drugs given after challenge. In this test, PKC inhibitors showed a moderate effect, in the same range as methotrexate, whereas dexamethasone suppressed the reaction. The ability of trifluoperazine in inhibiting cutaneous DTH reaction, depending on the treatment schedule and the hapten challenge dose, has been determined.