ADA enzymatic activity in PBMC and % deoxyadenine nucleotides in erythrocytes. ADA enzyme activity in PBMC was measured biochemically. The graphs show (A) the values from subjects not receiving busulfan conditioning and remaining on ERT (201-204) and (B) the values from subjects having ERT withdrawn and receiving busulfan before transplantation (301-306). The normal reference range for the ADA enzyme assay in human PBMC is indicated (gray-shaded horizontal bar). (C) Adenine and deoxyadenine metabolites were measured in erythrocytes by high-pressure liquid chromatography and the percentage that were deoxyadenosine nucleotides (dAMP + dADP + dATP) were plotted as %dAXP for the subjects in the group receiving busulfan (301-306). The times when ERT was resumed for subjects 304 and 306 are indicated.