Heat capacity measurements were made on p-bromoiodobenzene and p-diiodobenzene from 5 K to 380 K and from 5 K to 420 K, respectively. The measurements were used to calculate the entropy and enthalpy values relative to 0 K. The enthalpy of melting of p-bromoiodobenzene was found to be (19375 +/- 20) J.mol(-1), and the triple-point temperature, (363.52 +/- 0.01) K. For p-diiodobenzene these values were respectively (22328 +/- 50) J.mol(-1) and (402.40 +/- 0.05) K. A small solid-solid transition occurs in p-diiodobenzene. The maximum of this transition was measured at 327 K for sublimated material and shifted to 322 K for crystallized material. The enthalpy of transition was found to be (223 +/- 10) J.mol(-1).