The catechol-O-methyltransferase (COMT) val(158)met single nucleotide polymorphism (rs4680) has been shown to be associated with brain activation during a number of neurocognitive and emotional tasks. The present study evaluated genotypic associations with brain function during measurement of cognitive stability (prosaccades) and plasticity (antisaccades). A total of 36 healthy volunteers were genotyped for rs4680 and underwent functional magnetic resonance imaging (fMRI) at 1.5 T. Individuals with at least one val(158) allele (val(158) carriers, N=24) showed lower blood oxygen level-dependent (BOLD) response in ventromedial and dorsomedial prefrontal cortex during antisaccades compared to val(158) noncarriers, whereas met(158) homozygotes (N=12) showed lower BOLD response in a cluster in the posterior cingulate and precuneus during prosaccades compared to val(158) carriers. These findings suggest that associations of COMT val(158)met genotype with brain function may be mediated by task characteristics. The findings may be compatible with a hypothesis on the role of COMT val(158)met genotype in tonic and phasic dopamine levels in brain and differential effects on cognitive measures of stability (eg prosaccades) and plasticity (eg antisaccades).