Transfer of plasmid DNA to Pinus taeda L. (loblolly pine) cotyledon cells by microprojectile bombardment has been demonstrated using beta-glucuronidase (GUS). GUS histochemical staining indicated active enzyme in localized centers (blue spots) 24 hours after bombardment. GUS expression declined during subsequent culture, but remained detectable in meristematic tissue 62 days post-bombardment, however, transgenic shoots were not recovered. Localized GUS expression events resulted predominantly from single-cell events containing one microprojectile. The staining pattern was complex, with indigo found both in the central target cell and in adjacent cells. Cellular damage sustained by GUS-positive cells ranged from undetectable to sufficiently extensive to cause cell death. Microprojectile bombardment provides a useful method to assay transient gene expression in loblolly pine and has potential for the production of transgenic plants in pine.