In order to establish a noninvasive, quantitative method for measuring regional cerebral blood flow (rCBF) by N-isopropyl-p-[123I]iodoamphetamine (123I-IMP) SPECT, we attempted to employ continuous venous sampling instead of arterial sampling. Forty two patients with cerebrovascular diseases were classified into two groups, with (group II: n = 35) and without (group I: n = 7) hand warming. In group II, either hand was warmed, wrapping in a hot blanket (group IIA) or immersed in a 44 degrees C water bath (group IIB). In each patient, immediately after intravenous bolus injection of 222 MBq IMP, arterial and venous blood samples were collected continuously for 5 min from the radial artery and the cubital vein, respectively. By octanol extraction, IMP was divided into the unmetabolized and metabolized fraction. The ratio of 123I-IMP radioactivity of venous blood compared to arterial blood (pass ratio, referred as %PR) was calculated in three fractions, whole blood, unmetabolized, and metabolized fraction. By using these parameters, we assessed the possibility to estimate the amount of unmetabolized IMP fraction of arterial blood, usually used as an input function, from venous samples. In group I, %PR demonstrated a considerable variation between individuals (whole IMP, 47.5 +/- 24.6% (mean +/- SD): unmetabolized IMP, 46.0 +/- 24.5%: metabolized IMP, 51.8 +/- 27.4%). In group II, especially in group IIB, both increase of %PR value and the decrease in variation (whole, 77.9 +/- 5.6%: unmetabolized, 75.7 +/- 5.7%: metabolized, 86.7 +/- 8.7%) were observed, which permitted the further calculation based on the assumption that %PR value was constant in each IMP fraction (whole blood and unmetabolized fraction).(ABSTRACT TRUNCATED AT 250 WORDS)