This study developed and validated a bioassay for ramoplanin in human, dog, rabbit, and rat sera. Mean analyte recoveries and coefficients of variation for duplicate assays with each serum using coded and spiked (30-720 ng/ml) samples ranged from 93.5% to 106.3% and from 1.8% to 5.4% respectively. All correlation coefficients were > 0.99 and, for each serum, there was no significant difference in overall analyte recovery between the 2 test days.