A boy and a girl born to a consanguineous Tunisian couple are suffering from a slowly progressive nervous disorder. Initially they both had normal psychomotor development with acquisition of gait and speech. First symptoms in the boy were athetoid movements during the second year of life. He later lost all motor and language skills and developed muscular rigidity and intention tremor. At the age of five years, he was completely bedridden while he appeared mentally much less affected. His younger sister followed a similar course. The major specific abnormality detected was a strikingly elevated excretion of 2-oxoglutaric acid, which was identified by gas liquid chromatography, mass spectrometry, and enzymatic analysis. 2-oxoglutarate dehydrogenase activity in homogenates of cultured skin fibroblasts was reduced to about 25% of control values in both children. Although the pathogenetic mechanisms leading to brain damage remain obscure, the finding strongly suggest an autosomal recessive neurometabolic disease with predominant involvement of the extrapyramidal system.