Abstract 1. 1.|Temperature effects on the in vivo-incorporation of N-[ 3H] acetylmannosamine into brain gangliosides and sialoglycoproteins as well as of [ 3H] leucine into brain proteins were investigated in goldfish ( Carassius auratus) under different incorporation- (Intracranial or intra-ocular injections) and acclimation-conditions. 2. 2.|The incorporation of [ 3H] leucine into proteins was slightly reduced at 7°C in comparison to 20°C-conditions. 3. 3.|The radioactive NeuAc-labelling of glyproteins was reduced to about one-half and that of gangliosides to as little as one-fifth at the lower temperature. Concommittantly, at 7°C higher amounts of non-incorporated low molecular label occurred compared with the amount found at 20°C. 4. 4.|Due to the decreased incorporation of label and an additional diminishing effect of the lowered temperature on the rapid axonal transport, the renewal of gangliosides in the nerve endings of the optic tract was negligible at 7°C. 5. 5.|Pattern analysis showed that the inhibitory effect of lowered environmental temperatures on the brain ganglioside metabolism was even more pronounced in the poly-sialogangliosides compared with their less sialisated homologues.