Shown is median adhesion of RBCs from men with HbSS, and A. a history of priapism, under ambient (529, range 5–5248) or hypoxic (3268, range 49–18368, P=0.004, N=14) conditions in vitro, or B. without a history of priapism, under ambient (402, range 14–785) or hypoxic (122, range 31–4112, P=NS, N=12) in vitro. Shown also is adhesion of RBCs in this population, analyzed according to history of Hb desaturation in vivo, C. under ambient (440, range 16–5248) or hypoxic (4000, range 171–21576, P=0.001, N=15) conditions in vitro, or D. no known history of Hb desaturation, under normoxic (494, range 5–785) or hypoxic (102, range 31–521, N=11, P=N.S.) conditions in vitro.