Positive-ion electron impact (PIEI), positive-ion chemical ionization (PICI) and negative-ion chemical ionization (NICI) mass spectra of 19 phenothiazines are presented. In the PIEI mode, peaks due to M, M minus side chain (M - R1), M - R1 + H, and side chain itself (R1) appeared for most compounds. The M - R1 and R1 ions were very useful for drug screening. In the PICI mode, most spectra showed base or intense peaks due to M + H, and small peaks due to M + C2H5; peaks due to M - R1 + 2H and R1 also appeared in many compounds. In the NICI mode, fragmentation modes were different in different compound groups; molecular or [M - H]- quasi-molecular anions appeared in many compounds with aliphatic side chains. Anions at m/z 98 and 115 were characteristic for compounds with (N-methylpiperazinyl)propyl side chains. Selected ion monitoring in the PIEI mode generally gave much higher sensitivity than in the PICI and NICI modes. Phenothiazines present in urine or plasma could be rapidly isolated by use of Sep-Pak C18 cartridges. Thirteen of 19 phenothiazines could be detected by HP-17 wide-bore capillary gas chromatography with satisfactory separation from impurities in their underivatized forms.