As for the minor venereal diseases, the recognition of lymphogranuloma venereum is based first on clinical signs and confirmed by a group of laboratory tests. Ordinary cultures show nothing useful: the LGV agent grows like a virus, best in the yolk sac of fertile hens' eggs. The agent can be identified microscopically. The common confirmatory method is an allergic skin test ("Frei test"), which is done by injecting killed LGV agent obtained commercially. A tiny amount injected into the skin so as to raise a small bleb, with a control injection in the other arm of yolk sac material without LGV (to eliminate allergy to egg), shows, in positive cases, a pea sized swelling only in the test arm after two or three days. The test becomes Positive a week or so after infection starts, and remains positive permanently with or without treatment.

There is also a blood test for LGV based on antibodies to the agent. Both Frei and blood tests have a tendency to be positive in related nonvenereal diseases, including psittacosis, or parrot ever (a form of pneumonia), and trachoma, a serious disease of the eyes. These diseases are clinically so different from LGV that there is seldom any problem in distinguishing between them. Yet another member of the group known as TRIC agent is found fairly often in nongonoccocal urethritis.

The diagnosis of chancroid is confined by demonstration of its bacillus in the soft chancre either microscopically on a stained slide, or, better, by means of a culture, which can be done without special difficulty.

Granuloma inguinale is usually diagnosed by identifying the distinctive so called "Donovan bodies" inside the cells in material taken from the sores. The microbe can be cultured, but the technique is difficult and is not used much. A blood test for antibodies to the microbe also exists but, again, is seldom done.