Copurification.org is a resource for curating and analyzing the results of protein co-purification experiments. Copurification.org stores experimental details, in particular the protein extraction and sample washing conditions of the experiment, and cross-references these metadata to the obtained banding patterns, which constitute a kind of molecular signature of the experiment. Copurification.org enables users to compare different experiments conducted under different experimental conditions, side-by-side. We currently curate Saccharomyces cerevisiae, Escherichia coli, Mus Musculus and Homo sapiens genes and proteins. Copurification.org also provides tools to annotate SDS-PAGE gels with results obtained by western blot and protein identification by mass spectrometry.