The presence of 17β‐19‐nortestosterone (nandrolone, NT, 17β‐19‐NT) and its epimer 17α‐19‐nortestosterone (epiNT, 17α‐19‐NT) was investigated in the urine of six untreated boars, obtained from experimental farms. The presence of 17β‐19‐nortestosterone was screened by RIA and HPTLC and confirmed by GC‐MS analysis. Additionally, the two epimers (NT and epiNT) were investigated in the urine of a boar (two‐year‐old miniature male pig weighing 50 kg) before and after injection of 100 mg Laurabolin®(nortestosterone laurate, Intervet N.V, Belgium).