Sucrose density gradient purified plasma membranes isolated from brown adipose tissue of cold-acclimated hamsters (4-10 weeks at 0-4 C) were analysed for the content of the short (G s S) and long (G s L) variants of G s protein (the subunit of the stimulatory G protein) and compared with the membranes isolated from control animals. The relative ratio between the two variants (G s S/G s L) decreased from 0·48 to 0·24 (P<0·01). This result, obtained by electrophoretic resolution of membrane proteins by standard SDS-PAGE and an immunoblot analysis with an antiserum oriented against an internal sequence of G s , was verified by resolution on urea-containing gels and an antiserum oriented against the C-terminus decapeptide of G s .Under these conditions, the G s S/G s L ratio was decreased from 0·41 to 0·31 (P<0·05). The total amount of both isoforms (G s S plus G s L) decreased to 83% (P<0·05) or 68% (P<0·01) by standard or urea SDS-PAGE respectively. These data demonstrate that cold-acclimation of hamster brown adipose tissue is associated with preferential decrease in the plasma membrane density of the short variant of the G s protein.This decrease was paralleled by an increase in the other plasma membrane constituents, [ 3 H]CGP12177 binding sites, [3 H]ouabain binding sites and Na,K-ATPase activity to 147%, 212% and 191% respectively.