Five loci have been identified in Saccharomyces cerevisiae whose function reduces suppressor activity in strains carrying ochre super-suppressor mutations. Recessive mutations which allow an increased level of suppression occur at these loci. In such mutants, termed allosuppressors, the serine-inserting suppressor SUPQ5 suppresses ochre mutations in a [psi−] background and Class I tyrosine-inserting suppressors are lethal or have a reduced viability. Mutations at two allosuppressor loci, sal3 and sal4, have a lethal interaction with one another and with the extrachromosomal determinant [psi+]. This interaction is expressed in the absence of any suppressor mutation. All the mutant alleles of one allosuppressor locus sal3 are cold sensitive. One allosuppressor mutation, sal4.2, is temperature-sensitive for growth, as well as for other aspects of its phenotypic expression; namely the expression of SUPQ5 and the lethal interactions with Class I super-suppressors, with [psi+] and with sal3. At low temperature (24 °C), sal3-sal4.2 double mutants weakly suppress the ochre mutation ade2.1, but do not suppress his5.2 or lys1.1. It is argued that the site of function of the products of these loci is ribosomal and that they are involved in chain termination at UAA codons. It is inferred that the [psi+] factor or its product affects protein synthesis by interaction with the ribosome.