REPLY: We thank our colleagues Nataf et al. for their comments. The experience mentioned in their letter seems to confirm our opinion that the rapid injection together with the relatively low specific activity of the 18F-DOPA tracer as produced by us generated a first-pass bolus effect and might have had pharmacologic activity. The catecholamine nature of this tracer then presumably caused massive release of serotonin from the metastases. Since this incident, we have performed around 100 whole-body scans using a slow injection over 3 min with saline and have not witnessed any reactions.