The Pin2 genes encode potato type II proteinase inhibitors that act against pathogenic attack. The first examples were found only in the Solanaceae family, but, using new EST and genomic data, we have found 11 homologous genes dispersed through almost the whole range of mono- and di-cotyledonous plants. In contrast to the repetitive precursor sequences of the Solanaceae Pin2 genes, the new homologs have only a single repeat unit. The gene family appears to have evolved from a single-domain ancestral gene through a series of gene-duplication and domain-duplication steps. A number of unequal cross-over and gene conversion events could explain the current gene and domain pattern of the Solanaceae Pin2 subfamily.