Increased Brain-uptake of 13llodo-labelled Amphetamines by additional De u te ri u m-Label I i ng SUMMARY N(isopropy1)-and N(isobuty1)-lodo-amphetamine were double labelled with 1311 and deuterium. The deuterium labelled radiopharmaceuticals showed in mice and rats a higher brain uptake and a lower blood concentration than the controls (injection of the 131 l-labelled amphetamine without deuterium). The deuterium effect ist not increasing with higher deuterium content in the radiopharrnaceuticals.