The image quality of temporal (mask mode) intravenous digital subtraction angiography is directly dependent on the shape of arterial time-concentration curves produced by the intravenous injection of contrast medium. Curves that are narrow and tall minimize motion artifact (misregistration) and maximize contrast enhancement (pre- and postcontrast differences). To determine the effects of rate and volume of injection of contrast medium on intravenous digital subtraction angiographic curves, ioxaglate (Hexabrix), a monoacidic ionic dimer, was injected into large mongrel dogs. Quantitative measurements of opacification were made over time in the femoral arteries using a modified General Electric CT/T scanner. Peak opacification was directly proportional to the volume of contrast medium injected. Curve width was not affected by increasing volume of injection. At rates below a critical point, slower injection rates produced progressively shorter and wider arterial time-concentration curves. Above that critical point, increasing the rate of injection did not affect either curve width or curve peak.