To correlate extractable boron (B), clay and organic carbon (C) content and soil pH, the contents of available B were determinated in 103 soil samples of surface soil horizons from soils of Rio de Janeiro State, Brazil, using azomethin-H after extraction by hot water method. The average content was 2.43 + 0.67 mg kg-1 of B with a variation from 1.31 to 4.50 mg kg-1. The correlation values between B and organic C (r = 0.29**) and B and clay (r = 0.27**) were both significant. The highest correlation was found between B and pH (r = -0.41**). The amount of available B was influenced by clay and organic C contents.
