14-membered macrolide compounds such as erythromycins are provided with functional groups at the 14- and/or 15-position by providing a 14-membered aglycone template and feeding it to a strain capable of hydroxylating it at the 14 and/or 15 position. The strain may be found by screening, selected from known strains (e.g. Streptomyces eurythermus DSM 40014) or produced by genetically engineering a strain to express a cytochrome P450 enzyme.