In the newt, Triturus cristatus carnifex (Laurenti), the spleen normally contains a reserve of erythrocytes which varies according to the respiratory condition of the animal. In chlorobutanol-anaesthetized specimens, histological analyses and in vivo observations following the injection into the bloodstream of fluorescent microspheres 10 mu m in diameter (Fluoresbrite(TM) YG, Polysciences Inc., USA) show that, in steady conditions, the stored red blood cells are not segregated in the spleen but pass through the organ with a very slow flow; their lime of transit in a spleen maintained in a state of maximum congestion is 41.5 +/- 14.2 minutes (mean +/- standard deviation.