The aim of the present study was to investigate the ultrastructural changes developing in histaminergic neurons of the brain of 24 outbred albino male rats-after administration of ethanol in the acute experiment (single intraperitoneal dose of 1 and 4 g/kg), subacute exposure (as the sole source of drinking at a dose of 4 g/kg for 7 days), or chronic administration (at a dose of 2-3 g/kg/day for 6 months). After alcohol administration histaminergic neurons were found to develop various ultrastructural changes of their nucleus and organelles. They reflect the processes of neuron destruction, as well as adaptive changes aimed at restoring and maintaining their functions. These changes were nonspecific and -depended on the dose, time after injection and duration of alcohol administration. In general they corresponded to the structural and histochemical changes observed at light-microscopic level.