OBJECTIVE: The intention of the study was to assess whether a unique daily specimen is adequate for prophylactic posaconazole TDM in haematology patients and if bioassay and HPLC produce similar results and could be equally used in clinical setting.METHOD: Serum specimens from thirty haematology patients were collected at the end of the first and second week of treatment, just before the morning dose, 2 and 6 to 8hours afterwards. Levels were measured by bioassay in 157 specimens and additionally by HPLC in 51 of them.RESULTS: Bioassay levels were correlated inter and intra daily, with no statistical difference between them, irrespective of the timing. The same was true for HPLC measurements. There was no statistical difference between bioassay (median: 1.60mg/L, interquartile range: 0.60-2.30) and HPLC levels (median: 1.16mg/L, interquartile range: 0.56-1.72), while they were significantly correlated.CONCLUSION: In clinically stable haematology patients, a random specimen on any day after steady state serum concentrations have been achieved is probably adequate in order to monitor posaconazole levels. In the case of monotherapy, a bioassay is an acceptable alternative to HPLC.