Quantification of β- and α-cell volume by immunostaining on pancreata revealed that at diabetes diagnosis, only few insulin-secreting β-cells remained in the residual islet remnants, and pancreata consisted mainly of α-cells with total β-cell volume (0.12±0.04 μl per pancreas) being only 15% of that found in age-matched normoglycemic NOD-scid mice (0.76±0.07 μl per pancreas). This evidence concerns the gene INS and diabetes mellitus.