To investigate the reversal effect of reduced glutathione (GSH) on suppression of NK cells by reactive oxygen metabolites (ROM) in K562 cells, interleukin-2 (IL-2) or mononuclear cell (Mo) was added in cultured cell line of K562 cells and NK cells, the yield of ROM and K562 cell suppression rate were observed. Then the histamine dihydrochloride (DHT) or GSH was added in the mixed cultured cell lines, the ROM production and K562 cell suppression rate were observed. The results showed that the ROM yield increased from 33.17 +/- 5.08 U/L to 223.59 +/- 9.41 U/L by IL-2, and K562 cell suppression rate increased from 65.56% to 85.89% by IL-2 (P < 0.01). The ROM yields were 389.79 +/- 43.83 U/ml, 456.74 +/- 42.77 U/ml and 601.42 +/- 21.92 U/ml respectively, and K562 cell suppression rates were 82.36%, 81.36% and 48.09% respectively, when Mo was added in the mixed cultured cell lines under ratios of E/Mo being 10/2, 10/5 and 10/10. When E/Mo was 10/2, DHT or GSH was added in the mixed cultured cell line ROM yield decreased from 389.79 +/- 3.83 U/L to 50.21 +/- 2.4 U/L or -3.58 +/- 9.49 U/L (P < 0.05) respectively. With increase of concentration of DHT or GSH, the ROM yield in the mixed cultured cell line decreased (P < 0.05), the K562 cell suppression rate increased from 82.53% to 94.64% or 96.39% (P < 0.05), the more ROM yield, the less K562 suppression rate (P < 0.05). When E/Mo is 10/5 or 10/10, the ROM yield decreased by the high concentration of DHT or GSH (P < 0.05), but the K562 cell suppression rate not increased by every concentration of DHT or GSH. GSH was as effective as DHT in the reversing ROM and increasing K562 cell suppression rate. It is concluded that GSH may reverse ROM and increase K562 cell suppression rate, and GSH is as effective as DHT, but GSH has less side-effect than DHT. Therefore, GSH would be better antileukemia immune adjuvant.