Cytoplasmic and nuclear ecdysteroid receptors from intermolt Orconectes limosus integument have been compared. The specificities as well as the KD values for three [3H]ecdysteroids are very similar in both preparations. Using a photoaffinity labelling technique, the molecular mass of the hormone-receptor complexes from both preparations was determined by sodium dodecyl sulfate-gel electrophoresis as 70 000 Da. The isoelectric points are about 6 in both cases. Nuclear receptor can be extracted by 0.4M KCl. The binding can be completely restored if cytosol from the same source is incubated together with nuclei and [3H]20-hydroxyecdysone, but not if denatured cytosol or bovine serum albumin is used.