Cervical maturation, dilatation and uterine contraction in imminent premature delivery are closely related to chemical mediators from activated granulocytes which infiltrate into the cervix. It is known that urinastatin (urinary trypsin inhibitor, UTI) inhibits many kinds of chemical mediators from granulocytes and macrophages such as granulocyte elastase (elastase) and interleukin 1. We examined the effect of a UTI suppository on uterine contraction and the elastase level in cervical mucus in cases of imminent premature delivery. We treated 43 cases of imminent premature delivery with tocolysis index 3 or 4 with 4 kinds of therapy: Group A (N = 12): ritodorine drop infusion therapy; Group B (N = 9): daily UTI suppository (1,000U) therapy; Group C (N = 14): daily UTI suppository + ritodorine drop infusion therapy; Group D: daily UTI suppository + ritodorine drop infusion + antibiotics (oral cepharosporine) therapy. The elastase level of cervical mucus before treatment was 0.76 +/- 0.40 micrograms/ml in group A, 0.93 +/- 0.43 micrograms/ml in group B, 0.85 +/- 0.40 micrograms/ml in group C and 0.90 +/- 0.41 micrograms/ml in group D. There was no significant difference between these groups. The elastase level in cervical mucus was 0.75 +/- 0.47 micrograms/ml in group A, 0.27 +/- 0.35 micrograms/ml in group B, 0.27 +/- 0.33 micrograms/ml in group C and 0.30 +/- 0.19 micrograms/ml in group D, respectively. The elastase level was decreased significantly in groups B, C and D. The time taken to depress uterine contraction was 65 +/- 66 min in group A, 375 +/- 336 min in group B, 70 +/- 64 min in group C and 58 +/- 53 min in group D, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)