Leaf starch was measured, by a specific enzyme method, in Lolium sp., Festuca arundinacea and Dactylis glomerata grown in the field and in contrasting temperatures of two controlled environments. Starch levels of over 4% of the dry weight and 50% of the total hot-water-soluble carbohydrate (TSC) were recorded. Levels differed significantly between and within species, but populations of each species from N. Europe amd Mediterranean regions were not consistently different. There was more starch in cool than warm conditions and it increased during light and decreased during dark periods. However, there was no consistent temperature effect on starch accumulation during 7 h light in several L. perenne plants. D. glomerata leaves contained more starch (over 4 %) but less TSC than L. perenne.