The effect of bacterial endotoxin (LPS) on lysosomal enzyme activities of fibroblasts from normals and mucolipidosis III patients was investigated. Exposure of normal fibroblasts to LPS for 24 hours resulted in enhanced intracellular activities of beta-glucuronidase, beta-galactosidase, alpha-L-iduronidase and beta-N-acetylglucosaminidase. Endotoxin also led to an increased extracellular activity of beta-N-acetylglucosaminidase. In contrast, mucolipidosis III fibroblasts did not show either intracellular or extracellular increase of lysosomal hydrolases after LPS treatment. Difference in cellular responsiveness to LPS may be related to the mechanism of LPS-cell interaction.