Lowering the temperature to subzero values apparently had no effect on the colour in the frozen or thawed state. On thawing the ratio of the λmax at 278 and 525 nm (α-crustacyanin) and 560 nm (β-crustacyanin) remained unchanged, ( Table 1), and all samples satisfactorily underwent the reversible colour shift at the usual temperatures and reversion rates. However, on the further standing of these samples in 50 mM buffer, pH 7.0 at 6–8 °C for 10 days, those that had been frozen showed traces of orange precipitate indicating the presence of some denatured material due either to the low temperature or low ionic medium.