A study of the de Haas‐van Alphen oscillations in the magnetic susceptibility has been carried out inp‐type PbTe andn‐type PbS. Measurements have been made on oriented single crystal samples with carrier concentrations of the order of 1018/cm3in pulsed magnetic fields up to 125 kgauss. The results forp‐type PbTe indicate that the valence bands have a maximum atk=0, and four equivalent maxima at the {111} Brillouin zone faces. The ⟨111⟩ ellipsoids have a longitudinal mass to transverse mass ratio of 6.4±0.3. From the temperature dependence of the amplitude of the oscillations we obtain a value of 0.043±0.006m0for the transverse effective mass. The data indicate that the (000) maximum and the (111) maxima lie within 0.002±0.002 ev of each other. The data also indicate an effective broadening temperature of about 8°K which is attributed to inhomogeneities in the carrier concentrations in the samples investigated. Preliminary results onn‐type PbS show a single isotropic Fermi surface cross section with a cyclotron mass of 0.14±0.04m0. The direct and indirect optical interband transitions are discussed in the light of these results.