The conformation–activity relationships for the biologically active polyketide, epothilone, have been determined. Computer-based molecular modeling and high field NMR techniques have provided the solution preferences for epothilones 1 and 2. For the C1–C8 polypropionate region, two conformational families, conformers 1 and 2, have been identified as having significant populations in polar and non-polar solvents. In the C11–C15 region, additional flexibility was observed and two local conformations have been identified as important, conformers 3 and 4. Epothilone analogues with altered conformational profiles have been designed and synthesized. Conformational analysis and the results of biological assays have been correlated to provide increased understanding of the biologically active conformation for the epothilone class of natural product. Conformation–activity relationships have been shown to be an important complement to structure–activity data.