The specific heat ${C}_{p}$ of praseodymium and neodymium metals has been measured between 0.4 and 4\ifmmode^\circ\else\textdegree\fi{}K in a ${\mathrm{He}}^{3}$ cryostat. After assuming, on the basis of earlier research, ${C}_{L}=0.554{T}^{3}$ (specific heat always given in mJ/mole \ifmmode^\circ\else\textdegree\fi{}K) and ${C}_{E}=10.5T$ for the lattice and electronic specific heats of praseodymium, the remaining ${C}_{p}$ was analyzed into a nuclear contribution ${C}_{N}=20.9{T}^{\ensuremath{-}2}$ and into a magnetic contribution ${C}_{M}$. If compared with Bleaney's calculations based on fully magnetized electronic states in the metal, our experimental ${C}_{N}$ shows that 2.0% of the sample was in a cooperative state, probably ferromagnetic, the rest of the metal being paramagnetic. ${C}_{M}$ was further separated into a Schottky contribution with an excited electronic level at 28\ifmmode^\circ\else\textdegree\fi{}K (ions in hcp surroundings corresponding to 50% of the sample) and into a smeared-out cooperative peak with a maximum at 3.2\ifmmode^\circ\else\textdegree\fi{}K. The entropy under the latter curve is 95 mJ/mole \ifmmode^\circ\else\textdegree\fi{}K as compared with the value $0.020\ifmmode\times\else\texttimes\fi{}R\mathrm{ln}2=115$ mJ/mole\ifmmode^\circ\else\textdegree\fi{}K which would be expected as a result of magnetic ordering in 2.0% of the sample. Both ${C}_{N}$ and ${C}_{M}$ thus suggest that 2% of the sample enters a cooperative phase below 3.2\ifmmode^\circ\else\textdegree\fi{}K. This mechanism to explain ${C}_{N}$ and ${C}_{M}$ must be considered as preliminary. Our value of ${C}_{N}$ is rather different from earlier results. A sample-dependent ${C}_{N}$ is consistent with the picture of ferromagnetic domains. Below 2\ifmmode^\circ\else\textdegree\fi{}K the specific heat of praseodymium can be written, with 1% accuracy, ${C}_{p}=4.53{T}^{3}+24.4T+20.9{T}^{\ensuremath{-}2}$. At higher temperatures ${C}_{p}$ cannot be represented by a simple power series. The magnetic contribution to the specific heat of neodymium is huge due to cooperative peaks at 7 and 19\ifmmode^\circ\else\textdegree\fi{}K; even at 1\ifmmode^\circ\else\textdegree\fi{}K ${C}_{M}$ represents 88% of the total ${C}_{p}$. Below 7\ifmmode^\circ\else\textdegree\fi{}K neodymium is antiferromagnetic. After adopting ${C}_{L}=0.502{T}^{3}$ and ${C}_{E}=10.5T$ an analysis gave ${C}_{N}=(7\ifmmode\pm\else\textpm\fi{}0.7){T}^{\ensuremath{-}2}$. This value is about 50% smaller than that calculated by Bleaney if full electronic magnetization is assumed. However, the splitting of the electronic levels is rather large in neodymium and one cannot assume that $〈{J}_{z}〉$ in a cooperative state tends to $J=\frac{9}{2}$, but rather reaches a lower limiting value at $T=0\ifmmode^\circ\else\textdegree\fi{}$K. This explains the smaller experimental ${C}_{N}$. Between 0.4 and 1\ifmmode^\circ\else\textdegree\fi{}K the specific heat of neodymium may be written with 1% accuracy ${C}_{p}=125.7{T}^{3}+22.5T+6.4{T}^{\ensuremath{-}2}$. The accuracy of these measurements is estimated as 1.5% at 0.4\ifmmode^\circ\else\textdegree\fi{}K and as 0.5% between 1 and 4\ifmmode^\circ\else\textdegree\fi{}K. While checking the performance of our cryostat the specific heat of copper was found to be ${C}_{p}=0.0510{T}^{3}+0.698T$.