Electrophoresis of human DNA fragments (approximately 1 x 10(5) to 1 x 10(7) bases in size) was conducted in a solution of uncross-linked polyacrylamide contained in a horizontally mounted 1 mm diameter glass tube and monitored by epifluorescence microscopy. In presence of the polymer, molecular conformations described as a "trailing network" of DNA and a globular "head" were observed. The migration velocity varies between species differing in the size of the "head", and in the ratio between the size of the "head" and that of the trailing "network". By contrast, in pure buffer, lambda phage DNA migrates in a globular form at a mobility consistent with known macroscopic data. When electrophoresis in the polymer solution of an agarose plug preparation of Schizosaccharomyces pombe DNA was carried out after melting at 70 degrees C, a migrating DNA-agarose complex was observed. The complex was not fully dissociated by an agarose-hydrolyzing enzyme (Gelase).