During teratologic trials, routine investigations of 4261 brains from rabbit foetuses, fixed in Bouin's solution and sectioned by Wilson's free-hand razor blade technique, revealed cyst-like spaces in the brains of 164 foetuses (3.8%). The cyst-like spaces, characterised by the absence of an epithelial or endothelial lining, were usually solitary and occurred mainly in the massa intermedia of the thalamus. The spaces were found almost as ofter in control foetuses as in those from treated animals. On the basis of histologic examination and different fixation techniques, involving a further 1430 foetuses, these cyst-like spaces, previously interpreted as strain specific brain malformations, can be regarded as fixation artefacts.