Calculations of the activity concentration of RaA (218Po) in the air within living rooms and in the outside air were made at 87 dwellings in England and Scotland. From these measurements together with a determination of the ventilation rate existing in the room at the time of the measurements, the rate at which 222Rn is emanating from room surfaces into room air in pCil-1 h-1, can be calculated. For the dwellings studied the mean emanation rate is 0.54 pCil-1 h-1 and on the basis of a mean ventilation rate of one room change per hour throughout the year and assuming an occupancy factor of 0.8 the population exposure rate for the population of Great Britain to the short-lived daughters of 222Rn is estimated to be 0.15 Working Level Months per year.