Objective: To evaluate the etiology of cervicitis using the recommended Canadian definition, and to evaluate the efficacy and tolerability of seven days of minocycline treatment, 100 versus 200 mg at bedtime.Design: Randomized double-blind study with initial microbiological evaluation, and intended follow-up through 12 weeks.Setting: Women attending the major sexually transmitted disease clinic in Vancouver and the major teaching hospital in Winnipeg.Population Studied: Women with cervicitis (inclusion criteria were an off-white or yellow colour of cervical mucus when viewed on a white-tipped swab, and a mean of 10 or more polymorphonuclear leukocytes per oil immersion [× 1000] field on Gram stain of cervical mucus). Fourty-four women were enrolled but two were excluded because of contaminated cultures.Interventions: Treatment with two identical appearing capsules of 50 mg (100 mg dose) or 100 mg (200 mg dose) of minocycline taken at bedtime with water for seven days.Main Results: Of the 42 evaluable women, Chlamydia trachomatis was initially isolated from 19 (45%) and Neisseria gonorrhoeae from four (10%). The study was prematurely terminated because of an unacceptable and significantly higher frequency of adverse reactions on the higher dose regimen of minocycline – severe reactions in one (4%) on 100 mg compared with six (30%) on 200 mg (P=0.05). Major reactions were dizziness, mood alterations and nausea. Clinical parameters, but not numbers of polymorphonuclear leukocytes, improved significantly irrespective of initial microbiology or the regimen received. Cultures became and stayed negative for C trachomatis in seven of eight on minocycline 100 mg and five of six on minocycline 200 mg. Both ‘failures’ had an intervening negative culture and were re-exposed to untreated sexual partners.Conclusions: Although not a definitive study in terms of proving efficacy of lower dose regimens, the results are consistent with efficacy and demonstrate the significant advantage of the lower dose regimen in terms of adverse reactions.