In continuing investigations of host genetic control of nodulation in the Rhizobium-chickpea (Cicer arietinum L.) symbiosis, three γ-irradiation-induced mutants resistant to nodulation by Rhizobium strain CC1192 were characterized. When root temperature was controlled under greenhouse conditions, mutants PM665 and PM679 produced effective nodules at 24°C, but nodulation was strongly suppressed (PM665) or eliminated (PM679) at 29°C. Wild-type parent P502 was effectively nodulated at both temperatures, but lacked nodules at 34°C. Mutant PM233 did not form nodules at any temperature tested. In trials with 16 other strains of Rhizobium that formed effective root nodules on P502, no nodules formed on PM233, and only a few nodule-like protuberances formed on PM665 and PM679 when roots were maintained at 29°. In addition to the non-nodulating (Nod−) phenotype, PM665 also produced ledlets with aberrant trichomes that were characterized by scanning electron microscopy. Genetic studies showed that recessive alleles at three different loci were responsible for the Nod− phenotypes in PM233, PM665, and PM679. Progeny from all crosses involving PM665 showed cosegregation of the Nod− phenotype and the aberrant trichome trait. On the basis of data presented, it is proposed that the symbols rn1, rn2, and rn3 be assigned to the loci producing the Nod− phenotype in mutants PM233, PM665, and PM679, respectively.