Routine results of personnel internal dose monitoring programmes at the Austrian Research Centre Seibersdorf are evaluated in accordance with the Recommendations of the International Commission on Radiological Protection (ICRP), and in particular those discussed viz - routine thyroid monitoring for radioiodine, showing recurrent intakes of 131I and a single intake of 125I, a known accidental ingestion of 90Sr followed up by urinalysis and a case of plutonium inhalation detected by urinalysis. Difficulties concerning sensitivity and accuracy of such estimations are shown to arise if the radionuclides are short-lived and if the detection limit of routine bioassay methods is relatively high. In these cases adherence to the proposed ALI values cannot be controlled satisfactorily by personnel monitoring only, and careful control of the working area is necessary to assure that ALI values are not exceeded.