Using a Ra-α-Be source and a small boron trifluoride chamber as detector, the ratio of the neutron absorption cross-sections of boron and hydrogen, σB/σH, has been measured by the integration method in water and in aqueous solutions of boric acid. The result iswith a statistical error of ±30. Subsidiary experiments have been made which fix at about 3% the upper limit of the systematic error caused by perturbation of the neutron density in the neighbourhood of the ionization chamber.