Non-budding mutants of Chlorohydra viridissima regenerate heads 6 h faster than Hydra attenuata and the number of tentacles per head is higher. The polarity in pieces from the gastric region is the more labile, the smaller the pieces are. In regenerates heads and tentacles form much more frequently than feet, giving rise to bipolar or multiheaded structures. Buds very seldom form under normal conditions, but they occasionally occur in regenerating animals with two cut surfaces. The higher head-forming potential in the mutant is paralleled by a higher head-activator concentration (20-fold in head, 4-fold in body), than in Hydra attenuata, which is not accompanied by an equivalent increase in head-inhibitor concentration (1.4-fold in head, 2-fold in body). The foot-activator concentration is slightly reduced (1.3-fold), the foot-inhibitor concentration is higher (1.6-fold) than in H. attenuata. The mutant is extremely insensitive to head activator, relatively insensitive to head inhibitor and foot inhibitor, but sensitive to foot activator.