The tracer method has been adopted to study stratified-dispersed flow in a horizontal pipe, 80 mm in diameter and 50 m long, operating at 5 Bar with nitrogen-water mixtures. The use of the tracer method in a horizontal pipe required the development of a specially designed test section, the related electronics and a data acquisition system. It has also been necessary to develop a tracer injection system, which has been designed in order to obtain uniform tracer concentration in the liquid film immediately after its injection. The main flow parameters which can be measured with the present experimental set-up are the circumferential distribution of the film height, flow rate and tracer concentration, the rates of droplet entrainment and deposition and the split of the liquid phase between the wall layer and the entrained droplets. The average tracer concentration data have been interpreted with a new three-field model of the liquid phase in the stratified-dispersed flow pattern. In the present formulation, the model holds for steady, fully developed flow conditions and is based on a one-dimensional description of the flow system. The data cover a limited number of flow conditions. (C) 2014 Elsevier Ltd. All rights reserved.