The heat capacities of the eight existing ternary lanthanum chlorides AnLaCl3+n (A is K, Rb, Cs) and the four binary chlorides ACl and LaCl3 were determined from 200 to 770 K with a power-compensated differential scanning calorimeter. The results are expressed in polynomials C(p) = a + bT + cT2. The measured C(p) values were used to form the differences DELTAC(p) = C(p)(AnLaCl3+n) - [nC(p)(ACl) + C(p)(LaCl3)] by either taking the heat capacities for the single compounds or by direct measurements of samples of the ternary chlorides compared with samples of the binary chlorides with the same composition. All the DELTAC(p) values proved to be zero and thus confirmed findings from e.m.f. measurements in the temperature range 600-850 K, which yielded temperature-independent enthalpies and entropies for the formation of the ternary chlorides from (nACl + LaCl3).