Two nonce-word studies examined German-speaking children's productivity with the Perfekt (present perfect) from 2;6 to 3;6. The German Perfekt consists of the past participle of the main verb and an inflected form of an auxiliary (either haben ‘have’ or sein ‘be’). In Study 1, nonce verbs were either introduced in the infinitival form, and children (seventy-two children, aged 2;6 to 3;6) were tested on their ability to produce the Perfekt, or introduced in the Perfekt, and children were tested on their ability to produce the infinitive. In Study 2 twenty-four children aged 3;6 were given the past participle form of nonce verbs to see if they could supply the appropriate auxiliary (based mainly on verb semantics). The results were that many children as young as 2;6 used past participles productively (more than used infinitival forms productively), but all children had much difficulty in supplying both auxiliaries appropriately. The current findings suggest that mastery of the Perfekt construction as a whole does not take place before the age of four and that frequency of exposure is an important factor in determining the age at which children acquire grammatical constructions.