Whole carrots (Daucus carota L.) and midrib tissues of iceberg lettuce (Lactuca sativa L.) were treated with 42 μmol·m-3 MCP, then exposed to ethylene. Exposure to 42 μmol·m-3 ethylene at 10 °C increased isocoumarin content ≈40-fold in both peel and pulp of nontreated carrots within 4 days, but treatment with MCP for 4 hours at 20 °C before exposure to ethylene prevented isocoumarin accumulation. Ethylene-induced acidity loss and respiration rate increase in carrots were also prevented by MCP treatment. Ethylene treatment (126 μmol·m-3) of lettuce at 6 °C had induced russet spotting >5% to 10% of the midrib tissue by day 3 and 30% to 35% by day 9, while pretreatment with MCP for 4 hours at 6 °C prevented development of russet spotting. The results indicate that ethylene-induced physiological disorders and quality loss in carrots and iceberg lettuce can be prevented by MCP treatment prior to exposure to ethylene. Chemical name used: 1-methylcyclopropene (MCP).