Slightly elevated serum dolichol levels have so far been demonstrated only in alcoholics. We now report two diseases with exceptionally high serum dolichol levels. They are autosomal, recessively inherited lysosomal storage diseases, aspartylglucosaminuria (AGU) and mannosidosis. In 16 patients with AGU the mean serum level of total dolichols (457 +/- 43 ng/ml) was more than two-fold when compared to healthy controls (170 +/- 4 ng/ml). In two patients with mannosidosis the levels were almost two-fold. The percentage distribution of the dolichol homologues with 18, 19 or 20 isoprene units did not differ between the patients and controls. The inclusion of an additional control group excluded the possible influence of mental retardation and imparied moving ability on the results. Elevated serum dolichols in patients with lysosomal storage diseases may reflect a disturbance in lysosomal function and serve as a diagnostic marker. The biochemical mechanisms leading to this phenomenon remain to be established.