Several integumentary tissues of brachyuran crabs separate from the exoskeleton (undergo apolysis) when exposed to low temperatures (0°C) for one hour or longer. Apolysis did not occur in crabs held at room temperature for the same length of time following the destruction of the subesophageal ganglia i.e., the phenomenon was not due to the death of the animals. Apolysis did occur in animals chilled following ganglionectomy. Cold-induced apolysis occurred in species of seven families of brachyurans distributed throughout tropical, North Atlantic, or Pacific Northwest habitats. Therefore, it is not merely due to chilling subtropical animals. Adult majid crabs, which are in terminal anecdysis, underwent cold-induced apolysis as did Bermuda land crabs, the latter in all stages ofthe molt cycle tested. Chilling in vitro also induced apolysis in isolated pieces of integumentary tissue. The biological significance of these observations is that the mechanisms underlying apolysis may be activated in the integument...