Buffer solutions SMP, diluted (1+1) SMP, diluted Woodruff (1+2), calcium acetate 0.50 - 0.25 and 0.125 N estimate very well the lime requirement to bring to 6,40 the pH of several latosolic and podzolic soil samples incubated with calcium carbonate. Twelve equations were calculated by the method of least squares for the relationship between the pH of the soil-buffer suspension and the lime requirement to bring soil pH to 6.40 as determined by incubation.