Aims This study investigated the potential synergy between erythromycin and nisin against clinical Group B Streptococcus (GBS) strains. Methods and Results The combination of erythromycin and nisin was examined for synergistic activity using checkerboard and time-kill assays against invasive and colonizing GBS strains. Additionally, the immunological effect of the antibiotic combination was investigated in vitro using human U937 cells and ELISA analysis. Checkerboard assays confirmed an additive effect when the antimicrobials were combined, while time-kill assays demonstrated a synergistic effect when antimicrobials were combined for invasive GBS isolates. Furthermore, a significantly lower TNF-alpha response (P < 0 center dot 05) was observed in U937 cells challenged with GBS when erythromycin and nisin were used in combination. Conclusions The results suggest that erythromycin and nisin can act synergistically to inhibit the growth of GBS. Significance and Impact of the Study Group B Streptococcus is the leading cause of invasive neonatal disease worldwide and is becoming increasingly more prevalent in adults. Resistance to some conventionally used antibiotics, such as erythromycin and clindamycin, continue to rise among GBS, indicating a need for alternative treatments. This study demonstrates the potential of an erythromycin-nisin combination for treatment of GBS infections and encourages further investigation of this treatment option.