Activity and kinetics of arylsulfatase A (ASA, EC 3.1.6.8) were analyzed in leukocyte homogenates derived from patients suffering from cerebral palsy. Lower ASA activity was found in the patients' leukocytes than in controls, as determined by spectrophotometry using chromogenic substrate p-nitrocatechol sulfate (p-NCS). Kinetic parameters, K(m) and v(max), for leukocyte ASA were determined from the dependence of initial reaction velocities on the p-NCS concentrations. A slight difference in K(m) values was found for leukocyte enzyme in cerebral palsy (0.26 mmol L(-1)) compared to the control (0.21 mmol L(-1)), whereas v(max) value for leukocyte ASA in disease reached only 58% of the control value. In addition, the presence of the most common mutations associated with ASA pseudo-deficiency (N350S, 1524+95 A>G) and metachromatic leukodystrophy (P426L) was detected in all investigated patients. Changes in activity and kinetic parameters of leukocyte ASA in cerebral palsy are most probably related to the decrease of enzyme concentration; the detected mutations might at least partially contribute to the observed changes.