The influence of isoflurane (Iso) on the synthesis of surfactant-related protein A (SP-A) of alveolar type II (AT II) cells in primary culture and after injury by H2O2 was investigated. AT II cells were isolated and purified from adult Sprague-Dawley rats and used for experiments after 32 h in primary culture. The cell cultures were randomized to six groups (n = 8 in each group): control group (no treatment), 0.28 mM Iso group, 2.8 mM Iso group, 75 microM H2O2 group, 75 microM H2O2 + 0.28 mM Iso group, and 75 microM H2O2 + 2.8 mM Iso group. Each group was continuously incubated for 3 h after administration of Iso and/or H2O2. The intracellular SP-A and the SP-A of the culture medium were measured with an enzyme-linked immunosorbent assay (ELISA). Iso significantly decreased the intracellular SP-A content and that of the culture medium, and aggravated the decrease of SP-A content induced by H2O2. These findings suggest that Iso itself may decrease SP-A synthesis of AT II cells in vitro, and aggravate the damage to AT II cells under peroxidation conditions.