The pathology of maldronksiekte, a sporadic neurological disorder of cattle caused by the ingestion of the plant Solanum kwebense in certain parts of South Africa, was studied in three chronic field cases. There was loss of cerebellar Purkinje cells with the remaining neurons either swollen or shrunken and showing degeneration and necrosis. Ultrastructurally, neurons with a swollen perikaryon showed depletion and empty dilated cisternae of granular endoplasmic reticulum. In a few Purkinje cells, the cytoplasm contained small numbers of lamellar and membranous bodies. In the shrunken neurons, the highly condensed cytoplasm contained distended Golgi saccules, dense clusters of granular endoplasmic reticulum and swollen mitochondria. Lectin histochemistry revealed that the cytoplasmic vacuoles in some distended Purkinje cells stained strongly with Canavalia ensiformis (ConA) agglutinin and weakly with Triticum vulgaris (WGA) and succinyl-WGA (S-WGA) agglutinin. The pattern of lectin binding only partially agreed with that reported in calves poisoned with Solanum fastigiatum, causing a presumed glycolipid storage disease. Apoptosis was not detected in neurons using a commercial deoxyuridine triphosphate nick-end labelling (TUNEL) method. The pathogenesis of the cerebellar lesions is unknown but the intoxication may have resulted from the inability of neurons, in particular Purkinje cells, to metabolise a plant toxin or cellular substrate.