Given the close resemblance of the ring A structure of prednisolone and prednisone on the one hand, and of androstadienedione on the other, the transformation of cortisol and cortisone into prednisolone and prednisone in cattle faeces was evaluated. A simple method that does not involve extraction but only the 1:100 dilution of cattle faeces, spiking with 400ng/mL cortisol, cortisone or cortisol glucuronide and incubation of the suspension, was used. The analyses were performed by HPLC-MS(3) to detect the supposed Delta(1) dehydrogenation of the glucocorticoids. The decision limits (CCalpha) and detection capabilities (CCbeta) were 2.0 and 3.0ng/mL for cortisol, cortisone and prednisolone, 3.0 and 4.0ng/mL for cortisol glucuronide and 7.0 and 10.0ng/mL for prednisone, respectively. Intra-day and inter-day coefficients of variation (CV%), were 5.6-6.2 and 5.2-6.6 for cortisol glucuronide, cortisol, cortisone and prednisolone, and 16.0 and 16.2 for prednisone, respectively. The recoveries were in the range 110-143% for all analytes. Regression coefficients (R2) were in the range 0.996-0.999 for all analytes. The results show the hydrolysis of the conjugated form and the dehydrogenation in ring A in diluted faeces. It is therefore predicted that urine contaminated with faeces may be positive for prednisone and prednisolone in the same way as they are positive for boldenone, i.e. as a result of microbiological dehydrogenase activity on cortisol and cortisone.