In the same year, he met Karl Hoschna. They wrote a comic opera together, but no producer would pick it up, so they wrote songs to put in other Broadway shows. Isidore Witmark then contacted Hoschna, his employee, and told him he wanted to turn Mary Pacheco's play "Incog" into a musical. Hoschna then contacted Harbach, and so began the partnership. The result, with Whitmark and Charles Dickson writing the libretto, was "Three Twins", which opened in 1908 and ran for 288 performances (Harbach was paid a hundred dollars for his work). The show starred Clifton Crawford.