In April 1987 an intercomparison of radon daughter measurements was carried out by nine laboratories from Australia and Japan, using the radon test facility at the ARL, Melbourne. This work represents the Pacific region contribution to the phase 2 of the International Intercalibration and Intercomparison Programme for Radon, Thoron and Daughters Monitoring Equipment, for radon daughter measurement. This report describes the conditions and methodology used for these measurements. The results of the grab samples measurements of potential alpha energy concentration (PAEC) show that three of the laboratories were within 2% of the ARL determination. The PAEC results for the remaining laboratories were from 27% higher to 11% lower than ARL. Only the differences for two laboratories were significant at the 5% significance level. No significant differences were found between measurements of unattached radon daughters carried out by three of the laboratories. For the integrating monitors, the monitors based on nuclear track material were systematically higher by 27% to 65%, and the electronic monitors were between 8% high and 90% low. Some of the differences can be assigned to systematic differences in activity and flow calibration standards used by each laboratory. 10 refs., 22 tabs.