Copyright © 2016, American Society for Microbiology. All Rights Reserved. Our recent phase 1 trial demonstrated that PC-1005 gel containing 50 μM MIV-150, 14 mM zinc acetate dihydrate, and carrageenan (CG) applied daily vaginally for 14 days is safe and well tolerated. Importantly, cervicovaginal lavage fluid samples (CVLs) collected 4 or 24 h after the last gel application inhibited HIV-1 and human papillomavirus (HPV) in cell-based assays in a dose-dependent manner (MIV-150 for HIV-1 and CG for HPV). Herein we aimed to determine the anti-HIV and anti-herpes simplex virus 2 (anti-HSV-2) activity of PC-1005 in human cervical explants after in vitro exposure to the gel and to CVLs from participants in the phase 1 trial. Single HIV-1BaL infection and HIV-1BaL-HSV-2 coinfection explant models were utilized. Coinfection with HSV-2 enhanced tissue HIV-1BaL infection. In vitro exposure to PC-1005 protected cervical mucosa against HIV-1BaL (up to a 1:300 dilution) in single-challenge and cochallenge models. CG gel (PC-525) provided some barrier effect against HIV-1BaL at the 1:100 dilution in a single-challenge model but not in the cochallenge model. Both PC-1005 and PC-525 at the 1:100 dilution inhibited HSV-2 infection, pointing to a CG-mediated protection. MIV-150 and CG in CVLs inhibited HIV (single-challenge or cochallenge models) and HSV-2 infections in explants in a dose-dependent manner (P < 0.05). Stronger inhibition of HIV-1 infection by CVLs collected 4 h after the last gel administration was observed compared to infection detected in the presence of baseline CVLs. The anti-HIV and anti-HSV-2 activity of PC-1005 gel in vitro and CVLs in human ectocervical explants supports the further development of PC-1005 gel as a broad-spectrum on-demand microbicide.