Continuing a study of the magnetic rare‐earth hydroxides,1we have measured the specific heats of hydrothermally crystallized powder samples of Tb(OH)3, Dy(OH)3and Ho(OH)3between 0.6° and 18°K. Sharp anomalies associated with paramagnetic‐ferromagnetic phase transitions were found at 3.71° Tb(OH)3; 3.48° Dy(OH)3; and 2.54°K Ho(OH)3, in good agreement with the Curie temperatures deduced from magnetic measurements.1Analysis of the specific heats for Dy(OH)3and Ho(OH)3is complicated by Schottky contributions from low‐lying crystal‐field levels, and in the latter compound also by a large hyperfine contribution,Chf. However, for Tb(OH)3the ground state doublet is far below the first excited state which is at 170°K,2and the magnetic specific heatCmcould therefore be isolated by a simple analysis of the ``high'' temperature measurements to determine the lattice contribution, and a small calculated correction forChfat the lowest temperatures. The corresponding total entropy change is estimated to be (0.69±0.05)R, in good agreement with the expected valueRIn2. The highly anisotropic ground state1−3makes Tb(OH)3an unusually good approximation to an Ising ferromagnet, and this was confirmed by an analysis of the low‐temperature tail ofCm. A value for the energy of a single‐spin reversal atT=0°K is deduced: &Dgr;0=8.4±0.3°K, in reasonable agreement with the value 9.2±0.8°K estimated from the integrated specific heat and with the value 9.4±0.2°K obtained spectroscopically.2The reason for the apparent small discrepancy is not clear. Comparison of the experimental &Dgr;0with the calculated magnetic dipole contribution (&Dgr;0)dip=11.8°K shows that the ordering in Tb(OH)3is predominantly, but not exclusively, due to dipolar interactions. A similar situation was found for Dy(OH)3, where &Dgr;0=8.8±0.3°K was determined from the low‐temperature specific heat while the calculated (&Dgr;0)dip=13.3°K. For Ho(OH)3an accurate value for &Dgr;0could not be estimated, but it seems likely that the interactions are similar to those in Tb‐ and Dy(OH)3. Full details of this work are being published elsewhere.