HVA [homovanillic acid] and 5-HIAA [5-hydroxy-IAA] in CSF were determined in 5 patients with non-fluctuating progressive dystonia before and after treatment with L-dopa. The response to L-dopa was unequivocally favorable in 1 patient. The HVA-level in her CSF was significantly reduced before treatment, whereas in the other 4 non-responding patients the pre-treatment HVA was normal. The biochemical delineation of clinical responsiveness to a neurotransmitter may provide useful clues towards the classification of extrapyramidal disease in childhood.