Altogether 160 free living subjects (aged 30-60 years) most of whom had moderate hypercholesterolemia were randomised into the following diet groups to find out long-term effects of different fat-modified diets: (1) control diet 35/14:10:4 (energy percents from fat/saturated:monounsaturated:polyunsaturated fatty acids in actual diets); (2) AHA type diet 32/10:8:8; (3) monoene-enriched diet 34/11:11:5; (4) reduced-fat diet 30/12:8:3. LDL cholesterol fell equally with the AHA type diet (4.54 +/- 0.97 vs. 4.21 +/- 0.89 mmol/l (mean +/- S.D., 0 vs. 6 months), P = 0.001) and with the monoene-enriched diet (4.55 +/- 0.95 vs. 4.25 +/- 0.95 mmol/l, P = 0.004) during the 6-month study. Moderate amounts of polyenes or monoenes as part of natural diets did not decrease HDL cholesterol level in the long term. Serum lipid values remained unchanged with the reduced-fat diet. Analysis by apolipoprotein E phenotypes showed a decrease in LDL cholesterol only in subjects with phenotype 3/3 in the monoene-enriched group (-8.6 +/- 8.7 vs. +1.3 +/- 15.4, percent change in LDL cholesterol E 3/3 vs. E 4/3 + 4/4), but in the AHA type group LDL cholesterol decreased similarly in phenotypes E 3/3 and E 4/3 + 4/4 (-6.9 +/- 10.1 vs -6.9 +/- 16.5).