The plenary session of the Proteomics Standards Initiative of the Human Proteome Organisation discussed the current status of the ongoing work in the fields of molecular interactions, mass spectrometry and the description of protein modifications. In addition, new areas are being opened up, in particular developing standards for the description and exchange of data from gel electrophoresis experiments. The General Proteomics Standards group is now working closely with the Functional Genomics Experiment efforts to define a general standard in which to encode data that will enable a systems biology approach to data analysis.