A 96-well microplate assay that is used to determine the amount of cytochrome c in a human, mouse, rat or bovine sample. Cytochrome c is immunocaptured within the wells and the amount is determined by adding a cytochrome c specific antibody conjugated with horseradish peroxidase. This peroxidase changes the substrate from colorless to blue at 600 nm. This reaction takes place in a time dependent manner proportional to the amount of protein captured in the wells. The rate of development of blue color can be followed at 600 nm or the reaction can be stopped at a user defined time by the addition of 100 Ál of 1.5N HCl to each well (not supplied) and read at 450 nm. Included for the performance of this quantity assay are buffers, detergent, substrates, and 96-well microplate with monoclonal antibody pre-bound to the wells of the plate, allowing for a stream-lined assay.