The synthesis of cold shock proteins (csps) in response to cold shock, and of cold acclimation proteins (caps) in response to continuous growth at low temperature, in the psychrophile Aquaspirillum arcticum was investigated. With two-dimensional gel electrophoresis and computing scanning laser densitometry, cold shock treatments (10-degrees to 0-degrees-C, 5-degrees to 0-degrees-C, and 10-degrees to 5-degrees-C) induced a total of 14 csps, 6 of which were induced by all three cold shocks. The production of caps in response to continuous growth at 0-degrees-C was also found. Five of the 8 caps produced were also csps which suggests that these proteins may share a common involvement in cold adaptation.