This subseries consists of Lombardi's correspondence. The bulk of the general correspondence consists of letters from fellow researchers in the United States and Europe relating to Karl Heinrich Ulrichs, and the history of homosexuality in Germany and the Netherlands. The correspondents include Kent Gerard, Hubert Kennedy, and Jim Steakley in the United States, and Giovanni Dall'Orto, Wolfgang Kirchstein, and Eckhard Prinz in Europe. The materials also include personal letters from friends, including Los Angeles gay activist Don Amador, and from Lombardi's aunt Elena in Ireland. The Prometheus Books / Vern Bullough correspondence consists of letters relating to the publication and scholarly reception of Lombardi's translations of Hirschfeld's works, as well as Prometheus Books' 1994 publication of The Riddle of "Man-Manly" Love, Lombardi's translation of Ulrichs' collected Forschungen über das Rätsel der mannmännlichen Liebe. The materials include a large number of personal letters from Bullough.