Six soils of Piracicaba county. SP, Brazil, were tested and evaluated for assimilable boron by the sunflower biological method. The soils (Ibitiruna, Sertãozinho, Bairrinho, Pau d'Alho, Luiz de Queiroz and Guamium series) were found to be slightly deficient or non deficient in boron according to the Colwell criteria. The Pau d'Alho series showed to be superior to the other soils because the sunflower did not show response to boron. Sugar cane field plot and pot experiments in the same soils showed no responses to B addition.