A biokinetic model is presented that simulates the uptake and release of 99Tc by the European lobster (Homarus gammarus). This organism is of significant radioecological interest since lobsters, in contrast to most other organisms, have a high affinity for 99Tc. The model is designed to represent annually averaged 99Tc concentrations in lobsters from the Cumbrian coast, where significant levels of 99Tc have been released under authorisation by the nuclear fuel reprocessing plant at BNFL Sellafield. This paper describes the construction of the model, how it was calibrated using data from published literature, and preliminary results indicating that model output agrees well with the available monitoring data. Given that this model successfully combines laboratory and field data, this research could potentially make a significant contribution to the field, as, to date, it has been difficult to predict and explain concentrations of 99Tc in lobsters.