The Waxy (Wx) locus in maize determines the amylose content of pollen and endosperm tissue. There are several mutant alleles of the locus caused by insertion of transposable controlling elements. In the present study, we have used the properties of controlling element alleles to identify the Wx locus and its gene product, with the subsequent objective of isolating the elements causing the mutations. We present evidence that the Wx locus encodes a starch granule-bound 58 kd polypeptide that is synthesized in vitro as a 65 kd precursor. We describe the isolation of recombinant plasmids containing cDNA inserts homologous to Wx mRNA and a recombinant lambda phage containing a genomic Eco RI fragment encompassing most or all of the Wx transcription unit. We show that a mutation caused by the controlling element Dissociation (Ds) is attributable to an insertion of approximately 2.4 kb at the Wx locus.