Patterns of variation at selected isozyme loci were examined in populations of Cistus albidus L. in south-east Spain, from areas differing in precipitation and temperature, to determine whether population divergence has occurred. Total genetic diversity was high, with a high percentage of the variation being found between populations. Genetic variation between populations did not relate to climate. Populations exposed to severe summer drought did not show lower genetic diversity than populations from more benign climates. Little genetic variation was found between populations that showed variation in ecophysiological and growth responses in situ and under controlled conditions. Cluster analyses showed different patterns of between-population distances with respect to genetic, physiological and morphological data, and none of these patterns corresponded to that for between-site environmental variation.