We previously cloned the murine Penumbra gene based on its differential expression in proerythroblasts/erythroblasts. Subsequently, we identified human Penumbra cDNA from a human bone marrow cDNA library and the human Penumbra gene from a BAC library. Penumbra is a new member of the tetraspanin protein family and exhibits growth-suppressive activity in vitro. In this study, we designed a human Penumbra probe contig and used fluorescent in situ hybridization (FISH) to analyze seven cases of myeloid malignancies with 7q deletions. Five patients with cytogenetic deletions involving 7q31.2 approximately q32 also showed deletions of Penumbra by FISH; these were not present in two patients with cytogenetic deletions not involving 7q31.2 approximately q32. Our findings provide the first FISH evidence supporting the mapping of human Penumbra to 7q31.2 approximately q32 and demonstrate the potential of the Penumbra probe in the detection of 7q31 approximately q32-related deletions in myeloid malignancies.