The coffee diterpene cafestol occurs in both robusta and arabica beans. It is present in unfiltered coffee brews and raises serum concentrations of cholesterol, triacylglycerols, and alanine aminotransferase in humans. The effects are linear with the cafestol dose. Unfiltered coffee also contains the related compound kahweol, which occurs only in the major coffee strain arabica. The activity of kahweol is unknown. In a randomized, double-blind crossover study, we gave 10 healthy male volunteers either pure cafestol (61-64 mg/d) or a mixture of cafestol (60 mg/d) and kahweol (48-54 mg/d) for 28 d. Relative to baseline values, cafestol raised mean (+/-SEM) total serum cholesterol concentrations by 0.79 +/- 0.14 mmol/L (31 +/- 5 mg/dL), low-density-lipoprotein (LDL) cholesterol by 0.57 +/- 0.13 mmol/L (22 +/- 5 mg/dL), fasting triacy-glycerols by 0.65 +/- 0.12 mmol/L (58 +/- 11 mg/dL), and alanine aminotransferase by 18 +/- 2 U/L (all P < 0.01). Relative to cafestol alone, the mixture of cafestol plus kahweol increased total cholesterol by another 0.23 +/- 0.16 mmol/L (9 +/- 6 mg/dL) (P = 0.08), LDL cholesterol by 0.23 +/- 0.16 mmol/L (9 +/- 6 mg/dL) (P = 0.09), triacylglycerols by 0.09 +/- 0.10 mmol/L (8 +/- 9 mg/dL) (P = 0.20), and alanine aminotransferase by 35 +/- 11 U/L (P = 0.004). Thus, the effect of cafestol on serum lipid concentrations was much larger than the additional effect of kahweol, and the hyperlipidemic potential of unfiltered coffee mainly depends on its cafestol content. Both cafestol and kahweol raised alanine aminotransferase concentrations, and their hyperlipidemic effect thus seems not to be coupled with their effect on liver cells.