We have shown previously that supplementation of inflammation-inducing factor with a high dose of morphine inhibits intraperitoneal accumulation of exudatory cells in representatives of fish but not in amphibian species, and in some but not all strains of mice. In a case of mice, males were ip injected with zymosan (40 mg/kg, Z group) or with zymosan supplemented with morphine (20 mg/kg, ZM groups). At 4th hour of peritonitis, the total numbers of intraperitoneal leukocytes (PTLs), and numbers of polymorphonuclear leukocytes (PMNs) were significantly lower in ZM animals than in their Z counterparts in Swiss, C57C3H, Balb/c, and C57BL/6 strains but not in CBA mice. The aim of the present investigations was to monitor the time course of peritonitis (up to 24 hours) in Z and ZM groups of males of four strains. The results fully confirmed the lack of anti-inflammatory action of morphine in CBA strain. In Balb/c, C57BL/6, and Swiss mice, the number of intraperitoneal PMNs was lower in ZM groups during the whole investigated period, being statistically different during the first 12 or 8 hours. In a sharp contrast, the time course of intraperitoneal PMNs accumulation was very similar in Z and ZM groups of CBA mice.