It is proposed that tunable coherent radiation below 250 nm may be generated by sum frequency mixing the second harmonic output of a ruby laser and the output of a tunable IR laser in ammonium dihydrogen phosphate (ADP) and potassium dihydrogen phosphate (KPD). At 60 mJ pulse energies in input beams, a 30 mJ output pulse energy is obtained using a 25-mm long ADP crystal. This corresponds to a 1.0 MW output pulse power and an average output power of 30 MW. UV powers achieved with a 50-mm long KDP crystal are 20% larger than those for the 25-mm long ADP crystal. Overall efficiencies up to 4.0% for converting ruby-laser output radiation to sum frequency radiation are found. The technique has a variety of applications including the study of photoionization.