Anti-inflammatory activity and the mode of action of TAI-284 were investigated in animal models and compared with the activities of indomethacin. TAI-28 inhibited the increased vascular permeability in rats and mice which is the primary stage of inflammatory process, but the activity was less than that of indomethacin. The compound was as active as indomethacin in inhibiting acute rat paw edema induced by carrageenin and fracture. Furthermore, in the inhibitory effects on ultraviolet erythema in guinea pigs, durable paw edema induced by mustard and wound healing in rats, TAI-284 showed the same or more potent activity than indomethacin. Therefore, TAI-284 proved to have the same anti-inflammatory activity as indomethacin. TAI-284 protected rabbits from sudden death caused by intravenous injection of arachidonic acid, but the activity was about one twentieth less than that of indomethacin. The anti-inflammatory action of TAI-284 was derived from the mode of action of non-steroidal anti-inflammatory drugs, judging from the effects on ultraviolet erythema and death by arachidonic acid. On the other hand, the compound was more potent on secondary or thema and death by arachidonic acid. On the other hand, the compound was more potent on secondary or late stage than on primary stage of inflammation, and to some extent showed the mode of action seen with steroid antiinflammatory drugs. TAI-284 displayed marked inhibitory activity on nystatin induced paw edema in rats. It is suggested that the antinflammatory action of TAI-284 may be due to the lysosomal stabilizing effect.