Translocator protein 18 kDa (TSPO) is highly expressed in activated microglia and reactive astrocytes in brain, and it may, thereby, be a useful biomarker of neuroinflammation. We developed [(11)C]PBR28 as a positron emission tomographic (PET) radioligand to bind to TSPO and measure its density. Although [(11)C]PBR28 has high in vivo specific signal, it is very sensitive to the high and low affinity states of TSPO, which are caused by the rs6971 single nucleotide polymorphism (SNP) in the fourth exon of the TSPO gene resulting in a nonconservative alanine-to-threonine substitution in position 147 of the encoded TSPO protein. This co-dominant mutation yields three genetic groups: HH, HL, and LL, where H is the high-affinity form and L is the low affinity form. The frequency of the L allele is approximately 30%; thus, the frequency of the LL homozygote is approximately 9%. The affinity of PBR28 to H and L forms differs about 50 fold; thus, LL carriers provide no measureable signal in brain from [(11)C]PBR28. We recently developed a new TSPO ligand ER176, the affinity of which differs by only 1.2 fold and therefore LL carriers should provide measureable brain uptake. The purpose of this study is to assess the potential of [(11)C]ER176 to image TSPO in brain, characterize its binding sensitivity in lung of healthy subjects from all three genetic groups, and to do whole-body imaging for biodistribution and estimation of radiation dosimetry in humans.