To characterize the extraneuronal accumulation of catecholamines (CA) in the media of rabbit aorta pieces of isolated media were incubated with <sup>3</sup>H-CA (norepinephrine, isoproterenol or normetanephrine) plus <sup>14</sup>C-sorbitol (to estimate the extracellular space) for varying periods at 37 or 0 °C. The <sup>3</sup>H-CA accumulation was 1.3 ml/g at 0 °C and 2.2 ml/g at 37 °C. The sorbitol space was 0.6 ml/g at both temperatures. CA accumulation at 0 and 37 °C is significantly different from each other and from sorbitol accumulation. Corticosterone and phenoxybenzamine inhibit the temperature-sensitive component of CA accumulation. Accumulation of norepinephrine at 0 ° C is unaffected by corticosterone, phenoxybenzamine or oxytetracycline. The initial rate of NE accumulation at 37 °C, from steady state accumulation at 0 °C, and the initial rate of accumulation at 0 °C were linear functions of NE concentration between 10-7 and 10-2 M. Based on differences in sensitivity to corticosterone and temperature, we conclude that CA accumulation at 0 ° C is different from the accumulation at 37 °C.