The coverage-dependent heats of adsorption and sticking probabilities for CO on Rh{100} were measured. The initial heat is 118 +/- 4 kJ mol(-1), with an initial sticking probability of similar to 0.87; the saturation coverage is similar to 0.8 monolayer: By means of a Kisliuk fit to the sticking probability data, the transition between the two main adsorbate phases (c(2 x 2) structure at 0.5 monolayer and p(4 root 2x root 2)R45 degrees structure at 0.75 monolayer) could be detected, allowing the determination of two independent Kisliuk parameters for the first (K = 0.3) and second (K = 1) regime; The differential heat data was successfully reproduced by means of a Monte Carlo simulation. A discrete CO-CO interaction potential was implemented and optimized, giving CO-CO interaction energies of E-nn = 9 +/- 1 kJ mol(-1) (nearest neighbor), E-nnn = 1 +/- 0.5 kJ mol(-1) (next-nearest neighbor) and E-nnnn = -1 +/- 0.5 kJ mol(-1) (next-next-nearest neighbor). These energies agree well with the experimentally determined vm and nnn interaction energies and with a calculated CO-CO interaction potential (DFT) for CO on Pt{111}.