A 23-year-old woman and an 18-year-old man presented with severe pulmonary hypertension and subtle ground-glass lung opacities determined by CT scan. Open-lung biopsy in both cases showed PCH. Both patients subsequently underwent lung transplantation. We performed needle microdissection of nodules of PCH from cryostat sections, and then RNA extraction, probe preparation, and hybridization to oligonucleotide arrays (U95A; Affymetrix; Santa Clara, CA). We used unsupervised clustering in comparing PCH samples to the gene expression profile of healthy lung tissue.