Lipoprotein lipase (LPL) activities of postheparin plasma, heart, lungs, and adipose tissue, and salt-resistant lipase (hepatic lipase, SRL) activities of postheparin plasma, liver, and adrenals were examined in essential fatty acid deficient (EFAD) rats and in age-matched controls. The LPL activity of heart was higher in the deficient than in the control rats, but did not differ in the other tissues. The SRL activity of postheparin plasma was twofold higher, and that of liver and adrenals approximately 50% higher in the group with EFA deficiency. It is suggested that SRL exhibits an adaptive up-regulation in EFA deficiency. This up-regulation may be linked to a role for the enzyme in the transport of polyenoic fatty acids.