This is a study of the acquisition of prepositional case in a bilingua
l child, with special attention to the mutual import of linguistic the
ory on theories of language acquisition and vice versa. Another point
of interest is the nature of grammatical and lexical representations i
n bilinguals. I discuss the nature of lexical entries of German prepos
itions that assign two different cases and motivate my claim that the
main problem for the child is to establish the correct format for lexi
cal entries, and that the observed development can best be accounted f
or by a German-internal explanation, thus ruling out arty influence of
the child's bilingual situation.