In this paper, we describe the research using machine learning techniques to build a comma checker to be integrated in a grammar checker for Basque. After several experiments, and trained with a little corpus of 100,000 words, the sys tem guesses correctly not placing com mas with a precision of 96% and a re call of 98%. It also gets a precision of 70% and a recall of 49% in the task of placing commas. Finally, we have shown that these results can be im proved using a bigger and a more ho mogeneous corpus to train, that is, a bigger corpus written by one unique au thor.