The effect of ad libitum supplemental feeding upon the diet and foraging behaviour of red squirrels Sciurus vulgaris was studied in a coniferous habitat during May 1994 - July 1996. Although supplemental feeding in the form of peanuts was widely available, the animals continued to exploit natural foods such as pine seed, buds and flowers. The degree to which pine seed was exploited was a function of pine cone availability. In contrast, peanut consumption was not correlated with peanut availability, but was determined by the abundance of pine cones. During late winter and spring when seed was becoming scarce, peanuts contributed 30–56% of the dietary items. In addition, increasing amounts of alternative ‘low energy’ foods such as buds and flowers were also exploited. These foods are calcium rich and their ingestion would compensate for the high phosphorus content of peanuts. The nutritional composition of peanuts appears to have restricted the degree to which they could be included in the diet. Nevertheless peanuts were an important dietary component, and seasonally contributed 25–181% of the animals' basic daily energy requirements. Supplemental feeding was associated with relatively large amounts of activity occurring on the ground (annual mean estimates were 47 and 50% of total foraging time). The animals continued to exhibit ‘scatter-hoarding’ behaviour, with peanuts accounting for 90% of the identified cached items. This stored resource could satisfy 344 (1994/95) and 198 (1995/96) days of the animals' basic energy requirements.