The authors obtained theoretical and experimental data on the sensitivity to monochromatic and reaction neutrons of ionization chambers with different sizes of the air cavity between tissue equivalent walls. Significant difference of the sensitivity to neutrons of such heterogeneous chambers was noted as compared to that of homogeneous tissue equivalent ionization chambers. However proceeding from the results of the study we can determine with the precision of 10% the absolute absorbed doses in the dosimetry of biomedical investigations using neutrons of different energies.