This paper describes the determination of exchangeable calcium in soils, by the flame photometric method. A study was made concerning the interference of several ions on calcium determination by flame photometry. Iron, aluminum and phosphate interfere, when present in concentration considered high for the soils of the State of São Paulo, Brazil. In order to compare the flame photometric method with the permanganometric method for determining exchangeable calcium, five replications of ten soils were analysed by both methods. The ions that interfere (iron, aluminum, phosphate, etc.) were separated by ammonium hydroxide and bromine and the data obtained allow to conclue that the two methods are equivalente.