Absolute partial and total cross sections for electron-impact ionization of N2O, H2S, and CS2 are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ion species are collected with equal efficiency irrespective of their initial kinetic energies. Data are presented for production of N2O+, N-2(+), NO+, N+, and O+ from N2O; for production of (H2S++HS++S+) and H+ from H2S; and for production of CS2+, S-2(+), CS+, S+, C+, and CS22+ from CS2. The total cross sections are obtained as the sum of these partial cross sections. The overall uncertainty in the absolute cross sections for most of the singly-charged ions is +/-6-8%. For all three targets the cross sections for production of lighter fragment ions are found to be greater than previously reported which is consistent with the presumption of incomplete collection of energetic ions in the earlier studies. Agreement with recent theoretical calculations is satisfactory for N2O but not for H2S or CS2. (C) 2003 American Institute of Physics.