1. Recent studies have identified potential beneficial effects of eating nuts, most of which have substantial amounts of monounsaturated fatty acids (MUFA). Macadamia nuts consist of 75% fat by weight, 80% of which is MUFA (palmitoleic acid). 2. To examine variations in serum lipid levels in response to a high-MUFA diet based on macadamia nuts, 3 week interventions of macadamia nuts, coconuts and butter were determined in young, healthy Japanese female students. 3. After 3 weeks intervention, serum concentrations of total cholesterol and low-density lipoprotein-cholesterol were significantly decreased in the macadamia nut and coconut diets and bodyweight and body mass index were decreased in the group fed macadamia nuts, although there were no statistically significant changes in the group fed butter.