SummaryCounter‐diffusion coefficients of Rb86 and Sr89 counter diffusing against H+ ions were measured in Dundee silt loam and Sharkey clay soils at differing soil bulk‐densities. The cation exchange complex of each soil was saturated with either Rb+, Sr++, or H+ and washed free of salts before making diffusion measurements. The water content of the soil on an oven‐dry weight basis was maintained at a constant value for all bulk‐densities; 14.2 and 28.0 per cent for the Dundee and Sharkey soils respectively. These moisture contents correspond to a tension of 2/3 bar for sieved soil. The diffusion coefficients were dependent upon concentration. Average counter‐diffusion coefficients were calculated and related to soil bulk‐density.Soil compaction of Dundee silt loam had little or no effect upon the counter diffusion of Rb86. The average counter‐diffusion coefficients of Sr89 in Dundee silt loam and Sharkey clay were significantly and linearly related to bulk‐density; as bulk‐density increased the average counter‐diffusion coefficients increased. The average counter‐diffusion coefficients were approximately 0.5–0.75 of the corresponding self‐diffusion coefficients measured previously in these soils. The applicability of counter‐ and self‐diffusion data to practical field problems are discussed.