1. An earlier study had demonstrated that indomethacin, administered before E. coli endotoxin, abolished the initial pulmonary vasoconstriction and delayed the onset of the secondary shock phase that results from the intravenous injection of this agent in cats. The object of the present study was to determine whether indomethacin modified the shock phase when administered after endotoxin. 2. All the cats (whether or not they received indomethacin, 10 mg/kg) exhibited the characteristic features of the delayed shock phase that result from the administration of endotoxin (2 mg/kg). These included systemic hypotension, hypoglycaemia, reductions in arterial pH, cardiac output and systolic ejection time and an increase in arterial lactate. Five out of the ten animals given indomethacin survived 4 h compared with four out of twelve in the control (endotoxin along) group. 3. These results do not support the suggestion that antipyretic-analgesic drugs like indomethacin may be of benefit when given during bacteraemic or septic shock. They do support the suggestion that the acute pulmonary changes (hypertension and decreased compliance) that occur in this species within a few minutes of endotin administration ultimately contribute to the severity of the shock phase.