This paper investigates early productivity of morpheme use in Hungarian children aged between 2 ; 1 and 5 ; 3. Hungarian has a rich morphology which is the core marker of grammatical functions. A new method is introduced using the novel word paradigm in a sentence repetition task with masked inflections (i.e. a disguised elicited production task). Results suggest that Hungarian nominal and verbal suffixes can be used productively before the age of three. Children showed greater productivity with nominal than with verbal suffixes, and no productivity with novel suffixes; greater input variability facilitated productive use. These findings confirm that although morphological productivity is an early achievement, it is a gradual process influenced by several characteristics (e.g. syntactic category and variability) of the input. They also confirm that the new method is an effective way of testing morphological knowledge even at younger ages where other ways of eliciting grammatical knowledge often fail.