BACKGROUND: PHA (polyhydroxyalcanoates) are highly promising biopolymers, which are produced as storage material inside the cells by several microorganisms. During microorganism cultivations numerous parameters can be measured (DW, pH, glucose concentration, etc.) but the most important, e.g. PHA content in cells, can only be viewed by qualitative techniques or after long and tricky extraction for a quantitative approach. RESULTS: A thermogravimetric method was studied based on the difference between the degradation temperatures of PHA, at 210 degrees C, and those of the rest of the cells, the degradation of which begins at 250-260 degrees C. Proofs of the accuracy, robustness and reproducibility of this method were achieved. CONCLUSION: An optimized thermogravimetric method for PHA analysis inside cells has been described. This method allows a precise appreciation of PHA content in less than 70 min and with only 1 mL of withdrawn sample. (C) 2011 Society of Chemical Industry