Abstract 1. 1. The effects of noradrenaline (NA) and 5-hydroxytryptamine (5-HT), applied micro-electrophoretically from solutions of NA bitartrate, 5-HT hydrogen maleate, and 5-HT creatinine sulphate, were examined on spontaneously active and glutamate-excited neurons in the postcruciate cortex of anaesthetized (N 2O-methoxyflurane), cerveau isolé, and awake, non-paralysed cats. 2. 2. The predominant effect of both monoamines was one of depression. 3. 3. Artifactual excitation due to hydrogen ion effects was found when the monoamines were applied from solutions at pH 4·o or lower. 4. 4. Depressant as well as excitant effects of NA could be antagonized by the α and β adrenergic antagonists dibenamine, phentolamine, phenoxybenzamine, and d-INPEA, but 5-HT effects were often concomitantly blocked.