A method for aiding in selecting or adjusting a dose of TSPO imaging or therapeutic agent for use with a subject, the method comprising the step of determining the subjects genotype for TSPO rs6971. A TSPO imaging or therapeutic agent for use in TSPO imaging or therapy in a subject, wherein the subject is a subject whose genotype at TSPO polymorphism position rs6971 is determined. The subjects genotype for TSPO may be taken into account when assessing the results of the TSPO imaging, for example normalising the subjects determined measure of binding of the TSPO agent to take account of the subjects determined genotype. The subjects genotype for TSPO may be taken into account when choosing the TSPO agent and/or the dose of TSPO agent. The subject may be a subject who has been determined to have genotype CC or CT at TSPO polymorphism position rs6971, for example when using a TSPO agent that binds with higher affinity to Aia147TSPO than to Thr147TSPO.
