Serum lysozyme activity was determined in 135 healthy people classified into five different age groups ranging from 20 to 90 years. A turbidometric method with egg-white lysozyme as standard enzyme using the Fragiligraph for automatic recording of the serum lysozyme was used. The results show a progressive increase in serum lysozyme activity with age. In the oldest age group of 60–90 years, the increase in serum lysozyme was more than that expected for the diminished glomerular filtration rate in old age. Since the serum level of lysozyme can reflect the rate of neutrophilic turnover, it can be assumed that this rate increases above the age of 60.