The present study investigated children's early use of verb inflection in Japanese by comparing a generativist account, which predicts that the past tense will have a special default-like status for the child during the early stages, with a constructivist input-driven account, which assumes that children's acquisition and use of inflectional forms reflects verb-specific distributional patterns in their input. Analysis of naturalistic data from four Japanese children aged 1;5 to 2;10 showed that there was substantial by-verb variation in the use of inflectional forms from the earliest stages of verb use, and no general preference for past tense forms. Correlational and partial correlational analyses showed that it was possible to predict the proportional frequency with which the child produced verbs in past tense versus other inflectional forms on the basis of differences in the proportional frequency with which the verb occurred in past tense form in the child's input, even after controlling for differences in the rate at which verbs occurred in past tense form in input averaged across the caregivers of the other children in the sample. When taken together, these results count against the idea that the past tense has a special default-like status in early child Japanese, and in favour of a constructivist input-driven account of children's early use of verb inflection.