Paneth cell count correlates with GI GVHD clinical severity at onset. Mean Paneth cell counts per hpf (horizontal lines show mean of the means) were significantly different (P < .0001) in biopsies obtained at the onset of GI GVHD stage 1 (n = 69), 2 (n = 18), 3 (n = 12), and 4 (n = 16).