The 50th annual Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC), held in Boston, included topics covering new therapeutic developments in the field of infectious disease. This conference report highlights selected presentations on research with novel antimicrobial agents. Investigational drugs discussed include the dicationic porphyrin derivative XF-73 (Destiny Pharma), the tetracycline analog TP-434 (Tetraphase Pharmaceuticals), an elongation factor Tu inhibitor (Novartis Institutes for BioMedical Research), the dihydrofolate reductase inhibitor Rx-101005 (Trius Therapeutics), SII RMab, a fully human mAb to rabies glycoprotein (Massachusetts Biologic Laboratories/Serum Institute of India), the oral lipopeptide CB-183315 (Cubist Pharmaceuticals) for the treatment of Clostridium difficile-associated diarrhea, the phosphatidylcholine-specific phospholipase C (PC-PLC) inhibitor LMV-601 (Lumavita), and DS-003 (International Partnership for Microbicides), a small-molecule Gp120 inhibitor.