Between July and December, 1973, 340 new cases of syphilis previously unknown to the laboratory were diagnosed on the results of serological tests. The male-female ratio was 2-5 : 1. Homosexually acquired infections accounted for 34-3% of cases of syphilis in males. The cases were grouped into primary, secondary, latent and late stages of syphilis according to history, clinical signs and serological test results. Cases in each stage were subdivided into age groups. Primary and secondary syphilis (that is, the early infectious stages) occurred in 56 males and 23 females under 29 years of age. In 41 of the males (73-2%) this infection was homosexually acquired. The figures from this analysis show similar trends to those available in the United Kingdom.