As reported in Table , the prediction performance of the new implementation is comparable with that of FAME 3, for both 10-fold CV and the test set. The results indicate that, on average, for more than 80% of the annotated compounds (from the validation set and the test set as well), at least one known SoM is found among the two highest-ranked atom positions in a molecule. It is important to note that this value represents a conservative estimate because of the incompleteness of the metabolism data (which is not a limitation specific to this data set but to metabolism data in general). In other words, it is expected that many of the top-ranked atom positions will be considered to be false-positive predictions in this type of retrospective validation due to a lack of experimental observations and full reporting.