The main aims of this work were to examine in women: the relationship between the freely exchangeable Ca 2 + (FECa 2 + ) in the dense tubules and the activity of the sarco(endo)plasmic reticulum (SER) Ca 2 + -ATPase (SERCA) in platelets, and the relationship of these parameters with blood pressure and serum lipoproteins. Platelets from 14 white and 13 black women in good health were studied. The FECa 2 + was measured as the ionomycin-evoked Ca 2 + release (in the presence of thapsigargin) in Ca 2 + -free medium. SERCA activity was measured as the thapsigargin sensitive, Ca 2 + dependent and ouabain resistant, ATP hydrolyses in platelet membranes. Relative expressions of SERCA 2 and 3 isoforms and Ras-related protein (Rap) 1 in platelet membranes were determined by Western immunoblots. Highly significant correlations were observed for FECa 2 + in the dense tubules with: 1) the maximal reaction velocity (V m a x ) of the SERCA (r = 0.592, P = .0014), and 2) Rap1 (r = 0.551, P = .0035). In addition, negative correlations were observed between FECa 2 + in the dense tubules and age. No correlations were observed for these variables with blood pressure or serum lipoproteins. We conclude the FECa 2 + and the V m a x of the SERCA are reliable indicators of Ca 2 + load in platelets from women. However, in women, unlike previous observations in men, these platelet parameters are not correlated with blood pressure and serum lipoproteins.