A technique is described which allows reproducible preparation of liposomes with improved size-frequency distributions. The recent procedure of extrusion of crude liposome dispersions through controlled-pore polycarbonate membranes is used to control the upper limit of liposome diameter. Subsequent dialysis, using the same type of membrane, can remove the majority of liposomes smaller than a predetermined size. The pattern of dialysis of a liposome preparation is a function of the size-frequency distribution (as well as the membrane pore size) and can be used to approximate the distribution and/or used to monitor the reproducibility of liposome preparations.