Induced by too many wrongly determined specimens of Lactuca virosa L. the author discusses a number of differences with Lactuca serriola L. The fruit especially offers reliable characters (fig. 3). L. virosa probably occurs only as an alien in the Netherlands. In recent years L. serriola had a considerable expansion, particularly in the urbanized west of the country. Very often it concerns f. integrifolia Bogenhard. Nowadays, this forma seems to be more common than in former years.