The effect of small doses of ethylene glycol monomethyl ether (EGMME) on the activity of acetylcholinesterase (ACHE) in erythrocytes and whole blood as well as on the delta-aminolevulinic acid dehydratase (ALA-D) in blood and bone marrow was studied in Wistar rats. Significant reduction in the activity of both enzymes was noted three days after ip administration of 200 mg/kg b.w. EGMME whereas seven days later the activity of both enzymes returned to the control levels. Activity of ALA-D in blood appeared to be most sensitive to EGMME, and reacted even to the lowest dose, which did not significantly alter activity of ACHE or ALA-D in bone marrow. Haematological parameters in all treated groups remained unaltered.