Many laboratory tests of persons taking oral contraceptives are distorted. Elevations of binding proteins increase total plasma cortisol and thyroxine, although adrenal and thyroid function remain normal. Serum iron and iron-binding capacity are increased. Slight sulfobromophthalein and serum glutamicoxalacetic transaminase elevations appear to be innocuous. Serum immunoreactive insulin and growth hormone levels are elevated. Postprandial blood glucose and fasting triglyceride generally increase slightly, but the triglyceride rise may be profound in a hypertriglyceridemic woman. Renin substrate is generally elevated and aldosterone, occasionally. Significant hypertension, subsiding on withdrawal of the medication, has been seen rarely. Migraine may worsen, and cerebrovascular ischemic episodes and thromboses may occur, especially in hypertensives. The prevalence of thromboembolic episodes is increased, comparable with that of pregnancy. Melasma, benign cervical polyps, and vulvovaginal moniliasis are also seen. Cholestatic jaundice, marked triglyceridemia, positive lupus erythematosus preparations, hypertension, worsening migraine, or thromboembolism are contraindications. Morbidity and mortality due to oral contraceptives are low, and the risks of pregnancy often outweigh those of the pill.