The destructive effect on cells of locally injected hypertonic solutions, resorption of which is delayed by some vasoactive agents, was observed in the skin and subcutis of the rat by Selye and his coworkers who described it as acute conditioned necrosis. The same phenomenon was demonstrated in Walker 256 tumors implanted in the thighs of female Sprague-Dawley rats. A strongly hypertonic solution of glucose was injected once in and around the tumor (when it had reached a mean diameter of 1.5 cm), and 5-hydroxytryptamine was given s.c. at a distance. This resulted in disappearance of the growth in an average of 10 days and absence of metastases 2 months after treatment in 84% of animals as opposed to a spontnaeous regression of the tumor in 4% of control rats.