In epidemiological and ecological studies of radon as a health hazard in a given area or. region, it is becoming widely recognized that it is necessary to establish the significance of correlations, if any, between the incidence of diseases (e.g. lung cancer or leukaemias) and local radon concentration values. Measurements of soil-radon concentration levels in the field, especially under geostatistically controlled conditions, have underscored the highly erratic nature of radon emission on a scale often of only a few metres. It would appear that, while underlying geology does determine the longer scale of variation in soil-radon, many localized parameters, e.g. fissures, moisture content, thickness of overburden, etc., make it imperative that detailed in-situ measurements of radon emission are made before a reliable correlation can be established between say, leukaemia clusters and radon concentration levels. A broad survey of measurement methods and reported results, examined in the above context, is presented and conclusions drawn in this paper.