Hot water soluble boron content of six different soils of the State of São Paulo, Brazil, varies with the relationship between soil sample weight and water volume, keeping constant all other factors. So, when the extraction was performed using 2.5 grams of soil and 20 ml of hot water, the amount of soluble boron, expressed in ppm, was at least twice the amount extracted, with 10.0 grams of soil and 20 ml of hot water. On the other hand, the data obtained concerning to the extraction of soil soluble boron with 0.05 N acetic acid solution, shaking a 5 gram soil sample with 20 ml of solution for 15 minutes, seem to be reasonably good, but this technique merits further study.