INTRODUCTION: Aluminum phosphide (ALP) is used worldwide to fumigate grain. ALP poisoning, though reported from different parts of world, is most common in north, northwest and central India. In the presence of moisture, ALP liberates phosphine, which is highly toxic. The mechanism of action of phosphine is not known though experimental studies show that it inhibits cytochrome-c oxidase leading to inhibition of mitochondrial oxidative phosphorylation. PATIENTS AND METHODS: We estimated cytochrome-c oxidase activity in platelets of patients who had ingested ALP and compared them with those in healthy controls and in patients with shock due to other causes (cardiogenic shock, septic shock and hemorrhagic shock). RESULTS: After analysis of variance using Kruskal-Wallis test followed by Mann Whitney U test, significant inhibition of cytochrome-c oxidase activity could be found in ALP-poisoned patients compared to healthy controls (z = -5.513, p < 0.001) and in patients with shock due to other causes (z = -2.344; p < 0.05). There was no significant difference in inhibition in those who survived ALP poisoning compared to those who died from ALP poisoning (t = 0.02768; p > 0.05). CONCLUSION: Though inhibition of cytochrome-c oxidase in platelets does not have prognostic value, it suggests that interruption of mitochondrial oxidative phosphorylation as a result of cytochrome-c oxidase inhibition may lead to multi-organ dysfunction and therapeutic strategies to maintain enzyme activity may help in managing these patients.