The HS3 radical and the HS3- anion, the sulfur analogues of HO3 and HO3, have been detected for the first time by mass spectrometric experiments performed in the gas phase. The structural and energetic features of HS3 and HS3- have been investigated by ab initio calculations. Both HS3 and HS3- are characterized by HSSS open-chain structures, stable toward the dissociation into S-2 and HS0/-. HS3 acids to HS and HS2 as the known HSn species, and HS3- is the conjugate base of a strong Bronsted acid, the trisulfane HSSSH.