Transpositive mutagenesis was employed to prepare genetic strains useful in cloning the Virescent-1 locus (V1) of maize. A stepwise approach was used based on: (1) the isolation of putative insertion phenotypes (62 cases); (2) the verification of the genetic nature of the selected events (36 v1-m mutant alleles induced); (3) the accurate genetic study of 11 alleles; (4) the genetic assessment that the alleles v1-m1 and v1-m4 are due to the insertion of a Ds element into the locus V1; (5) the proof that a Ds-like DNA element induces the inactivation of the wild type function in the allele v1-m1. The phenotype of the unstable alleles, studied by germinating and keeping maize seedlings at the temperature of 18 °C, are the following: alleles v1-m1, v1-m9, v1-m11, v1-m17 and v1-m18 showing a few revertant green sectors on their leaves; v1-m4 exhibiting a reverse type of variegation; alleles v1-m2 and v1-m13 with a coarse pattern of variegation; alleles v1-m12, v1-m21 and v1-m23 frequently showing leaves part green with white stripes and part white with green stripes. For the alleles studied, in addition to somatic instability, germinal reversions also occurred. In some cases, these reversions resulted in stable derivatives with a different colour from that of the wild-type (‘near green’ or pale phenotypes). The results presented not only allow the v1-m1 allele to be chosen as a starting material for cloning the V1 locus, but also define the molecular strategy to be followed.