A method for inducing paralysis in embryonic chicks is described. This involves single injections of the neuromuscular blocking agents, D-tubocurarine Chloride or decamethonium iodide, into 10-day embryos. The dose which optimises survival and paralysis is determined along with the effect of the drugs on embryonic growth. Decamethonium iodide at a dose of 1 mg per embryo gave maximum survival and paralysis to 18 days of incubation. Paralysis was assessed by observation of treated embryos in ovo and by examination of embryos removed from their shells between 11 and 18 days of incubation. Embryos were completely paralysed 24 hours post-injection and remained paralysed until 18 days of incubation. Paralysed embryos failed to hatch. Development of the leg musculature was severely retarded in paralysed embryos. This method of inducing paralysis has considerable advantages over previous continuous infusion methods. The growth and collagen content of the tibia in the paralysed embryos was reduced and these results, and other applications of the method, are discussed.