Alpha-methyldopa or alpha-methylmetatyrosine (100 mg/kg) were administered orally to cats and the EEG recorded for 9 hours. Through the first 6 hours after each administration, the concentration of cisternal cerebrospinal fluid (CSF) 5-hydroxyindoleacetic acid (5-HIAA) selectively decreased from control (hour 0) while homovanillic acid (HVA) levels showed only small changes. On observation, the animals were quiet but awake. At 9 hours after alpha-methyldopa administration, the percentage decrease of 5-HIAA was significantly greater from the percentage decrease of HVA. The EEG record from 6-9 hours following either drug showed fewer intervals of EEG synchronization in both duration and frequency. These results indicate that behavior and EEG can be related to changes in brain monoamine metabolism determined in CSF. After either drug administration, dopamine turnover (as indicated by HVA) was higher than that of serotonin (as indicated by 5-HIAA) which corresponded to EEG desynchronization and other behavioral indicators of wakefulness.