A method has been developed for the isolation of temperature-dependent paralytic mutants of the nematode Caenorhabditis elegans, based on a screening procedure using short-time exposure to 30 degrees C. Of ten mutants isolated, eight lose their motilities between 30 degrees C and 33 degrees C without prominent changes in body forms. The other two strains that are mainly described in this report are accompanied by alterations in body forms. One mutation, cn101, is recessive and an allele of cha-1. The cn101 mutant shows reversible paralysis at 30 degrees, accompanied by a hypercontracted and coiled body form. At the restrictive temperature, the strain is resistant to all tested inhibitors of acetylcholinesterase (AChE). Another mutation, designated mah-2 (cn110), is a sex-linked semidominant that is mapped as 0.6 map units left of dpy-6. The cn110 mutant is rapidly paralyzed at the restrictive temperature and has a straight and rigid body form; the mutant rapidly recovers when the temperature is lowered. No disorganization of the muscle structure was detected by polarized light and electron microscopic inspection.