Parallelism experiments were carried out to determine if the recombinant human HSF1 standard accurately determines human HSF1 concentrations in biological matrices. Values were obtained using the cell supernatants from treated cultures serially diluted in assay buffer and assessed from a standard curve using four parameter logistic curve fitting. The observed values were plotted against the dilution factors. Parallelism of the curves demonstrates that the antigen binding characteristics are similar enough to allow the accurate determination of native analyte levels in diluted samples.