Submicrogram quantities of unstained proteins are visualized on polyvinylidene difluoride membranes by transillumination.

Unstained proteins on polyvinylidene difluoride membranes which have been dried and saturated with 20% methanol appear as clear areas when placed on a white light box. Sensitivity is comparable to that obtained with Coomassie Blue R250. This procedure greatly reduces the potential for unintended chemical modification during staining procedures, provides a nondestructive means of determining the major features of a protein pattern on a blot and makes it possible to initiate sequencing within minutes after blotting is complete.