Since the first description of the neck chamber technique for stimulating carotid baroreceptors by Ernsting and Parry in 1957, a number of different neck collars have been realized, among which the simplified version devised by Eckberg and coworkers in 1975 and the neck chamber described by Ludbrook and coworkers in our Institute in 1977. At variance with Eckberg's type, the "Milan neck chamber" completely surrounds the neck and allows the application of both positive and negative pressures to the neck by means of a system of double rubber valves that prevents air leakage from the chamber. The main advantage of this technique, as compared to infusion of vasoactive drugs, is the possibility it offers to study baroreflex control not only of heart rate, but also of peripheral resistance and blood pressure through neck chamber induced changes in carotid transmural pressure. In recent years a systematic evaluation of the neck chamber technique has allowed to clarify the following issues: 1) application of positive pressure to the neck, although increasing internal jugular venous pressure and thereby reducing the pressure gradient from the arterial versus the venous side of head circulation, does not reduce cerebral blood flow; 2) changes in pressure within the neck chamber do not seem to reduce blood flow to the carotid bodies, at least to a degree which might lead to chemoreceptor stimulation; 3) there is a linear relation between changes in neck chamber pressure and changes in tissue pressure adjacent to the carotid sinus. The transmission of pressure to pericarotid tissues is complex, however.(ABSTRACT TRUNCATED AT 250 WORDS)