We examined the influence of the K+channel opening drugs BRL 38227, pinacidil and diazoxide on cellular immune response and clinical course of experimental allergic neuritis (EAN) actively induced in Lewis rats by bovine peripheral myelin (BPM). T cell functions of EAN lymph node cells were assessed by measurement of proliferation and by counting of interferon-y secreting cells (IFN-γsc) in response to the specific antigen BPM and the T cell mitogen phytohemagglutinin (PHA). BRL 38227 and diazoxide at concentrations of 10-5M-10-6M and pinacidil at concentrations of 10-5M-10-7M enhanced the proliferative response to both BPM and PHA. The number of IFN-y sc was suppressed by the K+channel openers in the same concentration range. There was a tendency of stronger suppression of cultures with high numbers of BPM-reactive IFN-y sc than of cultures with low numbers of BPM-reactive IFN-γsc. The applied K+”channel openers are primarily acting on ATP-sensitivc K+channels, which have not been found in T cells so far. The drugs may, therefore, excert non-selective effects on conventional voltage-and/or Ca+ +-dependent channels of T cells.A first trial with in vivo administration of 2.5 mg/kg x day of the drugs resulted in more severe neurological deficits in the early phase of EAN with BRL 38227, whereas pinacidil and diazoxide had no significant effects.