We describe simplified and rapid methods to assess islet function with the aim to develop better protocols for islet isolation and to determine islet characteristics before transplantation. These methods are also useful in the assessment of the potentially beneficial or deleterious effects of compounds added to the culture media in stimulation experiments. To this end, we took advantage of the multiscreen assay system produced by Millipore SA. This 96-well unit allowed the free-floating culture of islets on filter membranes, the rapid vacuuming and collection of conditioned media or reaction buffer and thus successive testing of the same number of islets, possibly at different culture times. We estimated islet viability by determination of the metabolic activity of cells, normal function of islets by their ability to metabolize glucose and to synthesize and secrete insulin and of nitrite release, a reflection of nitric oxide (NO) status of cells, which may be involved in a signaling pathway during glucose-stimulated insulin secretion or in cytokine inducible pathway. Assays may be performed either on selected islets or on aliquots of semi-purified preparations designated for grafting, allowing thus the rapid estimation of graft function of the entire preparation. This herein described system may be also extended to many other functional tests.