1. Two different suspensions of radioactive particles, 99Tcm-labelled microspheres and 59Felabelled resin particles, were injected into the rat central circulation in order to study the distribution of blood flow to the skeleton. 2. Measurements of particle uptake showed that the mean proportion of cardiac output flowing to the skeleton was 3·1%, a figure much lower than the value of 27% found by Brookes (1970) in a similar experiment. 3. The blood flow per unit mass to individual bones covered a wide range.