Summary.A rapid reduction, after manufacture, in numbers ofRhizobium trifoliiin commercial legume inoculants was observed in 1971 and explained by the presence of high concentrations of sodium chloride in the peat used as carrier material. A strain ofR. trifoliigrowing in broth proved to be more sensitive to sodium ions than did 2 strains ofR. melilotibut was more tolerant of up to 0.3% of chloride. The effect of salt differed somewhat according to the source of peat used as carrier, but peat containing °0.2% of chloride (expressed as a % of dry peat) may cause considerable loss of viability of rhizobia