The molecular cluster ions HSO4-(H2SO4)(n-1) corresponding to the neutral species (H2SO4)(n) for n = 3-8 have been observed using a transverse chemical ionization scheme located inside a cooled flow tube. The contribution of ion-molecule clustering reactions was ascertained and readily separated from the ionization of the neutral clusters. The presence of the clusters was strongly dependent on temperature and humidity. Ratios of successive clusters thought to be representative of steady-state are reported.