A publication by Jakulj et al. ( 1 ) in this issue of the Journal of Lipid Research calls into question the validity of plasma noncholesterol sterols for the evaluation of cholesterol absorption in humans. This method was fi rst proposed by Miettinen and coworkers ( 2 -5 ), who showed that either sitosterol/total cholesterol or campesterol/lathosterol ratios refl ect amounts of cholesterol absorbed by the intestine. Normally only small amounts of plant sterols (sitosterol and campesterol) are absorbed, but Miettinen and associates claimed that quantities absorbed are proportional to amounts of cholesterol absorbed. In turn, the greater the total of plant sterol absorbed, the higher will be the plasma level, normalized for plasma cholesterol levels. These investigators ( 4 , 6 , 7 ) further showed that plasma levels of a cholesterol synthesis precursor, lathosterol, refl ect the body's cholesterol synthesis rate. Because absorbed cholesterol returns to the liver and suppresses cholesterol synthesis, a low level of plasma lathosterol will denote reduced cholesterol synthesis because of more cholesterol absorption. Consequently, the campesterol/ lathosterol ratio should better indicate cholesterol absorption than the sitosterol/cholesterol ratio. Jakulj et al. ( 1 ) attempted to validate plant sterols in plasma as a marker of cholesterol absorption. To do so, they compared plasma campesterol/cholesterol ratios with cholesterol absorption in mildly hypercholesterolemic subjects. Fractional absorption of dietary cholesterol was determined by comparing isotope ratios of plasma cholesterol following oral and intravenous administration. They found no difference in fractional cholesterol absorption in those with the highest and lowest campesterol/ cholesterol ratios. Nor was there a correlation between these ratios and fractional absorption in the total population. The authors concluded that previous studies claiming a relationship between plasma sterol ratios and cholesterol absorption are of questionable validity.It might be noted that Jakulj et al.( 1 ) did not measure a marker of cholesterol synthesis, e.g., lathosterol. Because of the inverse relation between cholesterol absorption and synthesis, the addition of a synthesis precursor could have helped to validate the use of noncholesterol sterols as a marker for cholesterol absorption as well as synthesis.The overall design of the study of Jakulj et al.( 1 ) nonetheless is of interest. Testing whether subgroups with the highest and lowest plant sterol levels have a different fractional absorption of cholesterol is innovative and worthy of further evaluation. On the other hand, methodological issues raised by this study deserve consideration.The method for measuring fractional absorption of cholesterol employed a dual stable-isotope method ( 1 ). ]sitosterol in sunfl ower oil by gentle heating and stirring before adding it to stomach-soluble gelatin capsules. Cholesterol absorption was determined by differences in isotope ratios between oral administration and fecal...