Islet cells derived from patients with persistent hyperinsulinemic hypoglycemia of infancy (PHHI) have the ability to grow readily in simple culture media. However, as with primary islets and cell lines, they lose hormone expression upon growth. In this study, we have investigated the role of three-dimensional cell-to-cell contact in the reinitiation of hormone expression in growth dedifferenti-ated PHHI-derived cells. Two main methods of cell aggregation were studied; the promotion of pseudoislets through petri dish culture and the creation of cell aggregates in the microgravity environment of the high aspect ratio vessel (HARV). Immunohistochemical analysis and ELISA assay showed that petri dish culture did not re-establish endocrine expression in any of the five cultures tested. However, through HARV technology, we have demonstrated that it is possible to reactivate insulin, glucagon, somatostatin, and GAD expression in PHHI-derived cells that had previously stopped expressing these markers. These results indicate that the unique environment of the HARV can be conducive to the upregulation of endocrine expression of islet-derived cells and optimization of culture conditions may prove useful in the sphere of β cell proliferation.