The recent identification of a gene residing at the mouse limb deformity (ld) locus permits us to test the hypothesis that disruption of this gene is responsible for an inherited anomaly affecting embryonic pattern formation. The gene gives rise to alternatively processed messenger RNAs that can be translated as a family of related protein products, termed the formins. We have now analysed transcripts from this gene in four independently isolated mutant alleles. In two of these, the ldHd allele (created by insertion of a transgene) and the ldIn2 allele (created by a translocation-inversion involving mouse chromosomes 2 and 17), a common subset of ld transcripts is abolished, but others are apparently unaltered. The correlation of altered transcripts in two independent ld mutants strongly supports the notion that one or more altered formins is responsible for the observed phenotype. That the defect is limited to the limb and kidney, despite expression of ld mRNA in other unaffected organs, suggests that these mutant alleles represent only partial loss of ld function.