The main challenge consists of determining whether peptide reactivity with antibodies is strong or weak, i.e., whether a peptide of the test set belongs to the positive or negative set. The goal is therefore to exploit the training set to develop a predictive model, taking into account the available information (e.g., the information on amino acids and protein-protein interactions available in biological databases). Participants are required to submit a ranked list of the peptides in the test set, ordered according to the predicted probability that the peptide belongs to the positive set (predicted reactivity).