  It is well known that for irreducible, square-integrable representations of a
locally compact group, there exist so-called admissible vectors which allow the
construction of generalized continuous wavelet transforms.
  In this paper we discuss when the irreducibility requirement can be dropped,
using a connection between generalized wavelet transforms and Plancherel
theory. For unimodular groups with type I regular representation, the existence
of admissible vectors is equivalent to a finite measure condition. The main
result of this paper states that this restriction disappears in the
nonunimodular case: Given a nondiscrete, second countable group $G$ with type I
regular representation $\lambda_G$, we show that $\lambda_G$ itself
  (and hence every subrepresentation thereof) has an admissible vector in the
sense of wavelet theory iff $G$ is nonunimodular.
