Aims To examine for psychrophilic or psychrotolerant micro-organisms in pharmaceutical cold rooms (in relation to numbers, incidents and species) and to determine, where such micro-organisms are present, whether standard microbiological environmental monitoring regimes require modification. This is presented as a case study. Methods and results Comparative environmental monitoring within different pharmaceutical facility cold rooms (using standard mesophilic and low temperature incubation). Data were collected over two periods, 5years apart. The results indicated that psychrophilic micro-organisms were not present and that those micro-organisms deemed psychrotolerant, primarily pseudomonads, could be grown on standard media under mesophilic conditions. Conclusions Psychrophilic micro-organisms were not detected and those considered to be psychrotolerant were only found in low numbers. Pyschrotolerant organisms were recovered under both low temperature incubation conditions and under standard conditions (between 20 and 35 degrees C). Further evaluation may be required, using alternative agar, and microbiologists should regularly review the species recovered to note differences between different environments. Significance and impact of the study The study came about from requests made by US and UK regulators concerning the risk of any extremophiles present in pharmaceutical manufacturing facilities upon product safety. Regulators expressed concerns about whether standard, and accepted, environmental monitoring regimes were capable of detecting such micro-organisms. The data provide a benchmark to support pharmaceutical manufacturers in relation to their existing monitoring programmes or as a case study with which to undertake a similar study.