This work is concerned with the dispersion of high-molecular-weight solutes in dilute solutions flowing through empty capillary tubing, such as that which is found between chromatographic columns and detectors, etc., in gel permeation or liquid chromatographs. Residence time distributions of solvent as well as solutes were measured simultaneously. This was done for both pulse and step solution inputs using a two-cell detection system. The solutes, o-nitrotoluene and narrow-distribution polystyrene (gel permeation chromatographic standards), were monitored with an ultraviolet detector while hexane (hexane-chloroform (20:80) was used to dissolve the polymer solutes) was monitored with a refractometer in a chloroform mobile phase. Polystyrene concentrations were 0.20 percent and 0.15 percent. Three tubing lengths and two flow rates were studied. The results indicate that polymer molecules have residence time distributions which are different from those of small molecules. This lends support to our belief that molecular entanglements occur among the polymer molecules which causes radial concentration non-uniformities and virtual two-phase flow. © 1971.