Several oxazine laser dyes have been studied at the air/water interface by the surface-specific technique of second harmonic generation.(SHG) spectroscopy. Oxazine 720, cresyl violet, and Nile blue readily form H-aggregate type dimers in aqueous solutions. We report an SHG study of the air/water interface of aqueous solutions of these water-soluble dyes in which it appears that the SHG signals originate almost exclusively from the dimers. The dominance of the dimer in the SHG process holds over a wide range of dye concentration and monomer-to-dimer ratios. The measurements were carried out with incident laser wavelengths near 600 nm, which are resonant with the first electronic transition, and include SHG spectra, solution composition dependence (i.e., dye concentration and salt (NaCl), surfactant, etc.), and polarization dependence. Addition of salt to the dye solutions increases the observed SHG signal intensity to a much greater extent (by as much as a factor of 30) than it promotes bulk aggregation. The SHG polarization dependence, i.e., the molecular orientation, remains unchanged. This suggests that the dimer concentration increases at the surface with the solution bulk ionic strength to a greater extent than for the bulk solution. The high concentration of dimers at the surface is consistent with the results of previous studies that reveal the less polar nature of the air/water interface relative to bulk water.