We have shown that LL-37, its truncated (GI-20, GF-17) and engineered (17BIPHE2) forms possess spermicidal effects and microbicidal activity against Neisseria gonorrhoeae. However, 17BIPHE2 has the highest spermicidal activity on human sperm resuspended in cervicovaginal fluid-containing medium due to its resistance to proteases. 17BIPHE2 should therefore be developed into a vaginal MPT agent. However, <5% of 17BIPHE2/LL-37/GI-20/GF-17 remained in the mouse reproductive tract after its intravaginal administration. A proper delivery formulation is thus needed. We have chosen the universal placebo gel, hydroxyethylcellulose (HEC), as an excipient in 17BIPHE2 formulation. HEC has been used safely as a vaginal lubricant and the uterus of mice injected with 2% HEC was still normal. 17BIPHE2 (32.4 or 86.4 µM) was solubilized in 2% HEC in a bicarbonate-5% CO₂ buffered isotonic salt solution (HEC-BS). 17BIPHE2-HEC-BS possessed in vitro spermicidal activity on mouse and human sperm. The contraceptive effects of 17BIPHE2-HEC-BS were then evaluated in mice. Since semen ejaculated in the mouse vagina is immediately swept into the uterine lumen, 17BIPHE2-HEC-BS was transcervically administered. Immunoblotting of uterine fluid collected from mice sacrificed 3 hours after transcervical injection indicated that 17BIPHE2 was present in a substantial amount, but the amount was decreased ~50% 24 hours after the administration. Through reaction with orcinol, HEC was shown to be present in the uterine fluid with amounts temporally declined like 17BIPHE2. Pregnancy of mice administered with 17BIPHE2 (86.4 µM)-HEC-BS was then determined. Only three of seven mice (43%) cycling in estrus, which were transcervically injected with 17BIPHE2-HEC-BS and then co-caged with fertile males for 3 days, became pregnant. In contrast, 100% pregnancy was observed in mice transcervically injected with HEC alone (n=5). While the results were promising, the experiments need to be done with more mice with modifications (e.g., with one-day co-caging with males and/or different percentages of HEC in formulation).