Embryonic midbrain micromass cultures were exposed for five days to ochratoxin A (OTA) at seven concentrations (ranging from 0.16 to 10 mu g/mL). Cell viability was assessed in neutral red uptake test (NRU), and differentiation - by immunoenzymatic determination of structural proteins (beta(III)-tubulin, MAP2, GFAP) expression level as well as by computer image analysis. Dose dependent decrease in cell number and differentiation was observed. Concentration-response curves were analysed and the mean inhibition concentrations (mu g/mL) for cytotoxicity (IC50) and differentiation (ID50) were calculated. There were no significant differences in the sensitivity of neurons in early and late stage of differentiation and astrocytes to the toxic activity of this compound. For all endpoints ID50 value was very low (< 10 mu g/mL) so OTA was classified as a strong teratogen. IC50/ID50 ratios < 2 pointed out that with harmful action of OTA the basic cytotoxicity should be connected.