The data concerning the distribution of Na+,K(+)-ATPase alpha and beta subunit isoforms in the spinal cord and partly in the motor neurons of the ventral horns are limited. The lumbo-sacral portion of the spinal cord of adult rats was immunotested with polyclonal antibodies (UBI, NY) specific for alpha 1, alpha 2, alpha 3 and beta 1, beta 2 isoforms. After paraformaldehyde perfusion and postfixation, free-floating 50 microns thick vibratome sections were immunostained with Vectastatin Elite ABC. Sites of bound primary antibodies were visualized by incubation in DAB-H2O2 substrate medium. The histochemical technique revealed immunostaining for all five isoforms of Na+,K(+)-ATPase in the motor neurons. The findings show a principal similarity in the distribution pattern of the immuno-like reactivity for alpha 1 and alpha 2 isoforms, the staining of the pericarya being more or less continuous with that of the microenvironment. The immunostaining for beta 2 (in comparison with alpha 1 and alpha 2) outlines the pericarya of the motor neurons slightly better, whereas the staining for beta 1 outlines them extremely sharply. The immunostaining pattern for the alpha 3 isoform differs considerably from that for the other isoforms. The immuno-like reactivity for this isoform is concentrated at the surface of the pericarya and processes of the motor neurons. Accumulation of alpha 3 immunoreactivity on the surface of the motor neurons might reflect the intensive traffic of the alpha 3 isoform from the pericaryon to the plasma membrane and the processes of the neurons. The findings from the investigations performed here support the opinion, that, in addition to the conventional catalytic role in Na+,K(+)-ATPase activity, Na+,K(+)-ATPase isozymes play a part in different specific phenomena in the nervous system.