The reduction of LAL activity in nine heterozygote, disease free carriers of mutations from two cholesteryl ester storage disease (CESD) pedigrees and the family of a patient with Wolman disease was associated with an increased fraction of monocytes which expressed CD56 (N-CAM) (4.1 +/- 2.7% of monocytes, compared to 2.2 +/- 0.5% in ten controls, P < 0.05), an antigen characteristic of immature myeloid cells, suggesting an increased turnover of monocytes.