Background: Parathyroid hormone-related peptide (PTHrP), identified as a tumor product, is responsible for humoral malignant hypercalcemia. Unlike PTH, PTHrP is found in almost every body tissue including pancreatic α, β, δ, and pp cells, where it is processed into multiple secretory forms, co-packaged with insulin, and secreted in a regulated fashion in response to insulin secretagogues. Ionized calcium is a stimulator for the release of several peptide hormones. Methods: In the present study, we examined the effect of an oral calcium (1 g elemental calcium) and glucose (75 g) load on insulin and PTHrP release in 16 healthy volunteers and of an oral calcium load in 16 non-insulin-dependent diabetes mellitus (NIDDM) patients. Serum calcium, glucose, insulin, and PTHrP levels were determined at 0, 5, 10, 15, 30, and 60 min. Results: Our results indicate that, at each time point, type 2 diabetic patients exhibited greater basal values of PTHrP than controls (200.3 ± 110.5 pg/ml vs. 82.0 ± 22.3 pg/ml, respectively, p < 0.0001). The PTHrP level was consistently higher in response to the glucose load than the calcium load at each time point observed (p < 0.0001). NIDDM patients exhibited greater basal serum PTHrP levels than the control group. Conclusion: PTHrP was proven for the first time to be released from β cells in parallel to insulin and in response to glucose stimulation.