The climate of the coastal region of La Serena, and the weather of the years 1950-55, is discussed with reference to the occurrence there of potato blight (Phytophthora infestans). The humidity requirements of the disease are met by the frequent wet morning fogs (camanchacas) following nocturnal dew; temperature also plays an important role. Rainfall is only a minor factor. Weather was particularly favourable to the disease in 1951; in the four following years it has been progressively less favourable. the danger of recurrence of suitable weather conditions is stressed.