Communicated by William S. Sly Gaucher disease is the most prevalent sphingolipidosis, characterized by genetic deficiency of lysosomal hydrolase glucocerebrosidase, and is inherited in an autosomal recessive manner. To characterize the molecular basis of Gaucher disease in Japan, we analyzed for the presence of the two known mutations (1448C and 754A) in the glucocerebrosidase gene of 15 patients (14 families) with Gaucher disease by selective amplification and restriction endonuclease analysis. W e found that the 1448C and 754A mutations occurred in all three clinical subtypes of Japanese Gaucher disease patients. T h e 1448C mutation was found on 12 (40%) out of 30 chromosomes (44% allele frequency in nonneuronopathic form, and 33% in neuronopathic forms), while homozygosity for this mutation was only found in two nonneuronopathic patients (age of 1 year 6 months and 7 years). We detected the 754A mutation on 6 (20%) out of 30 chromosomes. No patient was homozygous for 754A mutation. Furthermore, we identified four patients who were compound hetrozygote for 754A and 1448C. One of these was a type 3 Gaucher patient, but the other three patients were free from central nervous system manifestations at the time of observation. These results indicate that phenotypic presentation of Gaucher disease including the presence of nervous manifestation, progression, and severity of disease, may be affected by other genetic, environmental, or developmental factors, as well as the glucocerebrosidase genotype.