The pulsed photon activation (PPA) technique for nonintrusive measurements of single and two-phase flows in a horizontal pipe is developed. The advantages of PPA over pulsed neutron activation are discussed. Fluid velocity determinations using such a technique are carried out. An interesting subregion of the horizontal annular flow regime is found to have twin peak PPA time profiles. It is confirmed that these twin peaks are associated with the film flows on the upper and lower parts of the horizontal pipe, using the directionality of the PPA bremsstrahlung tagging beam. Film thickness measurements around the circumference of horizontal annular flows are also carried out using a resistivity needle probe, and analytical models involving droplet exchange and secondary vapor flow pattern are compared with the experimental data.