We used electrophoresis for three purposes: (i) estimation of the mean pore size of polyacrylamide gels via measuring electrophoretic mobility of globular proteins of known sizes in combination with simple sieve (cylindrical and slit) models; (ii) determination of the average size of protein molecules (native or denatured) by the use of the same models; (iii) monitoring the changes in molecular dimensions of proteins in the course of their denaturation. Both models yield results that are in good agreement with those found via the more elaborate techniques (considering the principal differences involved). The approach provides a direct and convenient way of monitoring the variations in protein sizes during the course of their denaturation in gels having a gradient of denaturants, and possibly the number of conformational states involved in the process, a facet that is quite unique and useful. The simpler slit model seems to yield better results in the latter case and is moreover supported by the recently reported data on electrophoresis of DNA molecules through the 1 mum slits of a microbrush matrix made of micropillars arranged in a hexagonal lattice.