We previously found no difference in healthy young adults' plasma cholesterols between palmolein and olive oil as the major dietary lipid, although the former is high in palmitic acid (16:0) but the latter in oleic acid (18:1 cis). In the experiment reported here we compared the effects of palmolein against another monounsaturated oil, highly oleic sunflower oil (HOSO), on plasma cholesterol in both young and middle-aged healthy adults. The test oils were provided as frying oil of potato crisps (150 g/day in men; 100 g/day in women) against low-fat background diets in free-living motivated volunteers. The design was a randomised double-blind 4-week/3-week crossover trial. Compliance was monitored with continuous dietary diaries and by measuring (fasting) plasma lipid fatty-acid pattern. Plasma lipids and vitamin-E compounds were measured at the start and twice at the end of each test period. In combined young plus older subjects (n = 42) mean plasma total and low-density-lipoprotein cholesterol (LDL-c) values were both 7% (significantly) lower on HOSO than on palmolein, but because high-density-lipoprotein cholesterol (HDL-c) was also 5% lower, the LDL-c/HDL-c ratio was only 3% lower on HOSO than on palmolein. The difference between the present results with HOSO and previous results with olive oil both compared against palmolein suggest that olive oil is associated with higher plasma cholesterols than other monounsaturated oils. In both the young and older subgroup, LDL-c was lower on HOSO but because HDL-c moved down too in the young subgroup, the LDL-c/HDL-c ratio was lower on HOSO only in the older subjects. Palmolein has an unusual pattern of E vitamins, with a high content of tocotrienols, notably the gamma-isomer. Unlike alpha-tocopherol however, there was no sign of these tocotrienols in subjects' plasmas.