The nuclear magnetic resonance of59Co nuclei in magnetic domains of RCo3(R:Y, Nd, Sm, Gd, Tb, Dy and Ho) has been measured under external fields up to about 50 kOe at 4.2 K. To assign the observed NMR signals to each Co site, the59Co nuclear magnetic resonance of R(Co1-xNix)3 and R(Co1-xFex)3 has also been measured under the same conditions. The results of NMR studies show that the cobalt atoms at the 6c site in the light R compounds(YCo3, NdCo3 and SmCo3) and these at the 3b site in the heavy R compounds(GdCo3, TbCo3 and HoCo3) have a large orbital contribution. © 1990 J.C. Baltzer A.G., Scientific Publishing Company.