Defects in mitochondrial oxidative phosphorylation are a feature of many human diseases. To date, determination of oxidative phosphorylation has required fresh and live sample material and therefore also access to specialized equipment and trained personnel. Cryopreservation of samples is an attractive alternative, where samples can be collected and stored in an economic and practical fashion for later bulk assays. Here, we present an accurate, reliable method for estimating mitochondrial oxidative phosphorylation capacity of cryopreserved human cells. Broad adoption of this method will allow uncomplicated collection of samples and measurements of oxidative phosphorylation.