Abstract: A new stable combination of Rhizopus arrhizus lipase and Pseudomonas fluorescens lipase for hydrolyzing triglycerides to free glycerol in body fluids is disclosed. Substantially complete and rapid hydrolysis is provided by a mixture of enzymes using a ratio between 2:1 and 10:1, about 5:1 being preferred, the amounts representing units of activity of each lipase. Approximately 150 units of total lipases will provide substantially complete hydrolysis of the triglycerides contained in 20 microliters of serum up to a minimum concentration of 5 g./l. within 2.5 minutes at 37.degree. C.