Inorganic and methylated germanium species were determined at sub parts per trillion levels by a combination of hydride generation and Inductively coupled argon plasma mass spectrometry (ICP-MS). The germanium species In solution were reduced to the corresponding hydrides by so dium tetrahydroborate, transferred with a helium gas stream, and trapped In a liquid nitrogen cooled U-trap. The hydrides were evaporated and Introduced Into the ICP torch, and the Ion count at m/z = 74 was monitored. The reduction efficiencies for methylated germanium species In a malic acid matrix were more than 97%. The absolute detection limits were 0.08 pg of Ge for Inorganic germanium (Ge1), 0.1 pg of Ge for monomethylgermanium (MMGe) and dimethyl germanium (DMGe), and 0.09 pg of Ge for trlmethyl germanlum (TMGe). The dynamic ranges of the detection span 4 orders of magnitude. The proposed method was ap plied to natural waters and wastewaters, and Ge1, MMGe and DMGe were detected In all of the samples studied. © 1991, American Chemical Society. All rights reserved.