A new series of thallium-containing materials, Tl1-xPbmATem+2 (A= Sb, Bi; m=10, 18; 0≤x≤0.3), has been prepared. Diffraction data reveal that a rocksalt-type structure is adopted at all compositions. Transport property measurements indicate n-type behaviour for the bismuth-containing materials and p-type for the antimony analogues. The reduced power factors for the latter, compared to the bismuth-containing materials, are primarily due to their more resistive nature. The highest power factors occur at a thallium deficiency in the range 0.1≤x≤0.2. Measured thermal conductivities are reduced from that of the binary telluride, suggesting that the materials may have potential as n/p-type components in device applications.