The incubation of 3alpha,7alpha,18-trihydroxy-ent-kaur-16-ene (7-epi-foliol) with the fungus Fusarium fujikuroi gave 3alpha,7alpha,18-trihydroxy-ent-kaur-16-en-18-al as the sole product. The biotransformation of other 7alpha- or 7beta-hydroxy derivatives had led to the oxidation of C-19, which is a main step in the biosynthesis of gibberellins and kaurenolides. Now, the presence of the 3alpha-hydroxyl impedes that oxidation, which is directed to the adjacent C-18 hydroxymethyl forming the corresponding aldehyde.