One hundred and fifty-four women with dyskaryotic cervical smears were referred for colposcopy from two distinct population groups, namely those who initially had attended a sexually transmitted disease (STD) clinic, and those who came from general practitioners and family planning and gynaecology clinics (non-STD group). They were investigated to determine the prevalence and pattern of concomitant lower genital-tract infections. The mean age in each group was 25 years. Microbiological studies revealed that 79 (51%) of the women were infected, more than one infection occurring in 16 (10%) of them. Infection was present in 40% of the non-STD group and 66% of the STD group. The pattern of infection was remarkably similar in each group. Bacterial vaginosis was the most common disease in each group and accounted for more than one-third of all infections detected. Six patients had genital warts, 15 harboured Chlamydia trachomatis and 4 had gonorrhoea. Two-thirds of those with C. trachomatis and half of those with gonorrhoea were asymptomatic. We conclude that an abnormal cervical smear is frequently a marker of concomitant lower genital tract infection. Comprehensive microbiological investigations in order to effect appropriate treatment are easily achieved on women in the STD group, but the cost may be seen as prohibitive for those in the non-STD group. For these women we suggest a less comprehensive microbiological approach that provides a compromise strategy of management.