Spermine (N, N'-bis(aminopropyl)-1,4-butanediamine) is a polyamine thought to be important in several cell regulatory processes. Previous studies had shown that spermine prevented the lateral diffusion of transmembrane proteins in human erythrocyte ghosts (Schindler et al. (1980) Proc. Natl. Acad. Sci. USA 77, 1457-1461). In this paper, we present results of studies on the effect of spermine on erythrocyte membranes by employing electron spin resonance spin-labeling techniques in conjunction with spin labels specific for skeletal proteins, bilayer lipids or cell-surface sialic acid of the membrane and by employing SDS-polyacrylamide gel electrophoresis analysis of extracted spectrin and Triton shells. The major findings are: (1) spermine significantly decreases the segmental motion of protein spin-label binding sites (P less than 0.0001), which are predominantly on cytoskeletal proteins; (2) addition of spermine leads to a significant increase in the rotational motion of spin-labeled terminal sialic acid residues (P less than 0.001), most of which are located on glycophorin A, a result which may be secondarily caused by spermine-induced aggregation of cytoskeletal proteins and the cytoplasmic pole of this transmembrane sialoglycoprotein; (3) spermine completely inhibits the low-ionic strength extraction of spectrin, the major protein of the skeletal network which is attached to the bilayer proteins by two or more connecting proteins; (4) pretreatment of ghosts with spermine followed by Triton extraction resulted in the retention of significantly increased amounts of Band 3 and other skeletal and bilayer proteins including Bands 4.2, 6 and 7 in Triton X-100 shells relative to that of control-treated ghosts. These results suggest that spermine acts both to increase protein-protein interactions in the cytoskeletal protein network and to bridge skeletal and bilayer proteins and are discussed with reference to possible molecular mechanisms by which spermine may influence cell functions.