After a preliminary study in 6 parkinsonian patients concerning the effectiveness and tolerance of 1,3-dimethyl-5-aminoadamantane hydrochloride (memantine) an investigation to assess its short-term effects was performed. In an unselected group of 12 parkinsonian patients 40 mg of memantine diluted in 500 ml of laevulose were applied i.v. within 2 h. The patients were examined under standardized conditions before, immediately after and 2, 4 and 24 h, respectively, using a program of physchological tests. The results give evidence for a favourable influence on rigor and tremor in Parkinson's syndrome as well as on motor drive. In comparative studies memantine showed a better tolerance than adamantylaminosulfate. The short-time effects of the drug could be differentiated from placebo and learning effects.