1. The respiratory role of the area postrema (AP) has been investigated in pentobarbitone- or alpha-chloralose-anaesthetized, vagotomized, paralysed and artificially ventilated rabbits, by means of electrical stimulation and microinjections of DL-homocysteic acid (DLH). Phrenic nerve activity was used as an index of central respiratory drive. 2. Bipolar electrical or chemical stimulation (microinjections of DLH, 5-30 nl; 160 mM) of the caudal compact portion of the AP provoked excitatory effects on the inspiratory motor output, without apparent changes in the arterial blood pressure. 3. Depressant effects on inspiratory activity, accompanied on some occasions by changes in arterial blood pressure (as a rule, increases > or = 30 mmHg) were induced by DLH microinjections in close neighbouring areas (including the medial part of the nucleus tractus solitarii) or in the IV ventricle. 4. These results support a role for the AP in the neural control of respiration. The findings are discussed in connection with other autonomic functions to which the AP has been reported to contribute, in different animal species.