Pancreatic lipase catalyses the hydrolysis of emulsified triglycerides to form a transparent solution of monoglycerides and fatty acids. Levels of serum pancreatic lipase were measured in neonates known to have cystic fibrosis and compared with levels in control infants. During the first weeks of life infants with cystic fibrosis had raised serum pancreatic lipase values in parallel with raised serum trypsin values. A simple and specific turbidimetric dried blood spot assay for serum pancreatic lipase was used as a screening test fo cystic fibrosis in the neonate.