A very simple procedure which enhances sensitivity in visualizing proteins stained by all standard procedures in polyacrylamide gels is described. The process, based on the use of concentrated polyethylene glycol 6000 solutions, produces a conspicuous, reversible, and uniform size reduction of gels. The entity of the reduction depends principally on the polyethylene glycol 6000 concentration and on the acrylamide content of gels. Using an appropriate polyethylene glycol 6000 concentration, it is possible to regulate the final size and then the sensitivity as needed. Depending upon the above conditions it is possible to increase the sensitivity by a factor of 4-6 or more. Reduction of the gel volume by such a factor may eliminate the need for the cumbersome and frequently impossible preconcentration of samples. Besides the Coomassie blue stained gels, silver stained gels may also be treated in a similar manner with a consequent further enhancement in sensitivity. In addition, gels containing radiolabeled materials can be autoradiographed in times proportionally shorter, without significant sacrifice of resolution.