Following a common practice in generative grammar, HPSG treats the determiners as members of a separate functional part of speech (Det). The status of the functional parts of speech is a matter of debate and controversy. The auxiliaries, for instance, are commonly treated as members of a separate functional category (Aux or Infl) in many variants of generative grammar, including GB, MP and LFG, but in GPSG and HPSG, it is a matter of equally common practice to treat them as members of V and to reject the postulation of a separate functional category, see Pullum & Wilson (1977) and Gazdar, Pullum & Sag (1982). This text makes a similar case for the determiners; more specifically, it argues that the determiners are categorially heterogeneous, in the sense that some are members of A, whereas others are members of N. The argumentation is mainly based on inflectional morphology and morpho-syntactic agreement data. The consequences of the categorial heterogeneity are hard to reconcile with the specifier treatment of the determiners in Pollard & Sag (1994) and with the Det-as-head treatment in Netter (1994), but it can smoothly be integrated in the functor treatment of the prenominals in Allegranza (1998) and Van Eynde (2002).