The dielectric functions of equiatomic XTi (X=Fe,Co,andNi) alloys in the B2 phase (cubic CsCl structure) were measured by spectroscopic ellipsometry in the energy range of 1.5-5.4 eV. The optical conductivity spectra show close resemblance to each other with a peak at 1.9-2.3 eV and another at 3.1-3.4 eV. Fine structures observed in previously reported measurements were not seen. The band structures and the optical conductivity spectra were calculated in the B2 phase using the linearized-augmented-plane-wave method with the local density approximation. The agreement between the measured and calculated spectra is markedly improved by the inclusion of a quasiparticle self-energy correction. Strong optical transitions are identified and the similarities and differences among the optical conductivity spectra of the three compounds are explained.