A schematic drawing illustrating the relative distribution of drug transporters, both influx and efflux pumps, in the seminiferous epithelium of adult rat testes. It is noted that both efflux pumps (e.g. P-glycoprotein) and influx pumps (e.g. OATP, OAT, and OCT) are found at the BTB and the apical ES, associated with the integral membrane proteins localized to either Sertoli cells at the BTB or Sertoli and elongating spermatids at the apical ES. Full colour version of this figure available via http://dx.doi.org/10.1677/JOE-10-0363.