A method for stimulating pancreatic cells to synthesize and/or excrete insulin comprises contacting insulin-producing cells, in particular their aqueous suspension, with a water-soluble cellulose derivative, in particular selected from alkylated, hydroxyalkylated, and alkylated-hydroxyalkylated cellulose or a mixture thereof. A medium for the culture of pancreatic .beta.-cells contains an effective cell-stimulating amount of a cellulose derivative. It can be used to stimulate pancreatic .beta.-cells to produce and/or excrete insulin. An apparatus for such stimulation comprises a container holding a solution of a cellulose derivative in an aqueous culture medium. Stimulation of pancreatic .beta.-cells by a cellulose derivative is useful in the management of diabetes. Further preservative or therapeutic methods using the aqueous cellulose derivatives are disclosed.