SPECT scanning using ⁹⁹Tc‐TRODAT‐1, a ligand that binds to dopamine transporters, may be useful for detection of early Parkinson's disease (PD), diagnosis of presymptomatic individuals, and monitoring disease progression. Understanding whether genetic factors contribute to inter‐individual variability is crucial for interpreting imaging results in the context of disease pathophysiology. We tested whether polymorphisms in the genes for catechol‐O‐methyltransferase (COMT), monoamine‐oxidase B (MAO‐B), and the dopamine transporter (DAT) influence dopamine uptake parameters in the striatum in vivo in asymptomatic volunteers and patients with PD as measured with ⁹⁹Tc‐TRODAT‐1. ⁹⁹Tc‐TRODAT‐1 binding declined with age in both asymptomatic volunteers and PD patients, and depended on disease duration in PD patients. We found no significant association between COMT, MAO‐B, and DAT polymorphisms and results of ⁹⁹Tc‐TRODAT‐1 testing in asymptomatic volunteers or patients with PD. In PD patients, the age of disease onset and speed of progression did not differ based on these polymorphisms. These results demonstrate that these specific genetic variations do not alter the fidelity of ⁹⁹Tc‐TRODAT‐1 as a measure of dopaminergic function in asymptomatic volunteer individuals or patients with PD. © 2003 Movement Disorder Society