Revertants of unc-15(e73)I, a paralyzed mutant with an altered muscle paramyosin, include six dominant and two recessive intragenic unc-15 revertants, two new alleles of the previously identified suppressor gene, sup-3 V, and a new suppressor designated sup-19(m210)V. The recessive intragenic unc-15 revertants exhibit novel alterations in paramyosin paracrystal structure and distribution, and these alterations are modified by interaction with unc-82(e1220)IV, another mutation that affects paramyosin. A strain containing both unc-15 and a mutation in sup-3 V that restores movement was mutagenized, and paralyzed mutants resembling unc-15 were isolated. Twenty mutations that interfere with suppression were divided into three classes (nonmuscle, sus-1, and mutations within sup-3) based on phenotype, genetic map position and dominance. The nonmuscle mutations include dumpy and uncoordinated types that have no obvious direct effect on muscle organization. Two recessive mutations define a new gene, sus-1 III. These mutations modify the unc-15(e73) phenotype to produce a severely paralyzed, dystrophic double mutant that is not suppressed by sup-3. Five semidominant, intragenic sup-3 antisuppressor mutations, one of which occurred spontaneously, restore the wild-type sup-3 phenotype of nonsuppression. However, reversion of these mutants generated no new suppressor alleles of sup-3, suggesting that the sup-3 antisuppressor alleles are not wild type but may be null alleles.