A highly sensitive LC-MS/MS method for the quantification of N,N-dimethyltryptamine (DMT) and its metabo­lites indole-3-acetic acid and DMT N-oxide in human plasma has been developed and validated. Chromatography was performed using a diphenyl column with gradient elution (0.1% formic acid in methanol/water). The mass spectrometer was operated in multiple reaction monitoring mode. A methanolic solution containing internal standards 2-methylindole 3-acetic acid and deuterated DMT, was added to plasma samples, followed by protein precipitation with acetonitrile. The samples were centrifuged and supernatants transferred to new tubes and evaporated to dryness before reconstitution in aqueous mobile phase. The method was validated with regards to accuracy, precision, sensitivity, selectivity, recovery, matrix effects, stability, carry-over and dilution integrity. The validated linear range was 0.25–200 nM for DMT and 15–250 nM for DMT N-oxide. For the endogenous compound indole-3-acetic acid a different approach was taken due to its significant presence in blank samples. The change in signal response from a blank sample was used when constructing the calibration curve with linearity demonstrated between elevations of 500–5000 nM above the blank. Applicability of the described method was demonstrated through analysis of plasma samples from healthy volunteers having received intra­venous injections of DMT. The presented method for rapid and sensitive quantification of DMT and its metab­ olites in human plasma can be applied to future studies aiming to characterize DMT disposition and its relationship to immediate psychedelic or long-term antidepressive effects.