QSAR classification models of human ADORA2a performed very well with Matthews correlation coefficient (MCC) ranging between 0.62 and 0.70 for cross-validation and 0.48 on the temporal test set (Figure ). Except for the human ADORA3 and rat ADORA3 that performed bad both during cross-validation and testing due to the imbalance of the datasets (ratios of 1:7 to 2:6 of actives to inactives for human ADORA3 Overall models on the AR subset showed similar performance between regression and classification. It is no surprise that the receptors that performed best, i.e. most of rat and human receptors, were those with the most datapoints.