SummaryFor an evaluation of effects of seasonal cold acclimation and evolutionary cold adaptation on protein synthesis capacity the protein synthesis apparatus was isolated from the gills and white muscle of Antarctic eelpout Pachycara brachycephalum and North Sea eelpout Zoarces viviparus. Both species had been acclimated to 0 (control) and 5°C (Antarctic) and 5 and 10°C (North Sea control), respectively. The translational capacities of the protein synthesis machineries were determined in an optimised cell free in vitro system. The results demonstrate that tissues from the polar zoarcid possess cold adapted protein synthesis machineries indicated by low activation energies, and, especially, high RNA translational capacities at similar RNA:protein ratios when compared to temperate zoarcids at 10°C. When both species were brought to 5°C, the temperate species displayed cold compensated protein synthesis capacities caused by elevated RNA:protein ratios. Warm exposure (from 0 to 5°C) of the Antarctic zoarcid revealed a capacity for thermal acclimation indicated by a reduction in protein synthesis capacities associated with lower RNA:protein ratios.