We studied the effect of seven different clinical diseases (viral infections, bacterial infections, malignant diseases, cardiovascular diseases, gastroenterological diseases, endocrinological diseases, and rheumatic diseases) as well as normal pregnancy on serum dolichol concentrations in 76 hospitalized patients and in 10 pregnant women. In contrast to urinary dolichols, serum dolichols were not significantly increased in any of these conditions, suggesting that dolichol levels in serum and urine are independently regulated. Furthermore, we found that serum dolichol concentration does not undergo diurnal variation, as in healthy volunteers time of blood sampling did not affect serum dolichols. Our results suggest that serum dolichol concentration, which has earlier been found to be exceptionally high in aspartylglucosaminuria and mannosidosis, might serve as a laboratory marker for these recessively inherited lysosomal storage diseases.