The lysozyme level was found to reach its highest point on the second day from parturition, followed by strong decline to a much lower value which then remained constant up to the 30th day of lactation. The rise recorded from the period between farrowing and the second day after birth as well as the decline up to the fourth day and the constant level up to the 30th day from parturition were statistically secured. Lysozyme levels in the milk of sows with no previous lactation record was found to be lower with significance than those recordable from sows with something between six and nine previous lactations. The conclusion has been that lysozyme levels are strongly affected by both lactation time and number of lactations. Lysozyme concentrations in sow milk on the first and second days from parturition were betweeen 6.8 and 11.0 microgram/ml, depending on the number of previous lactations. Such high lysozyme levels in sow foremilk over the first three days of age as well as all findings so far gained on the structure of bacterial cell walls are likely to suggest that the above enzyme affects bacterial population of the gastro-intestinal tract of suckling.