Two fluorometric assays for the determination of poly-beta-hydroxybutyrate (PHB) inside intact cells are presented in this paper, a spectroffuorometric method and one based on a laser flow cytometer. The principles of these assays are given, and the results of these methods are compared with those of a gas chromatographic assay. All assays were used for the monitoring of batch cultivations of Alcaligenes eutrophus. The correlation between all methods was very good; however, the fluorometric analysis was the fastest, while the cytometric assay gave a direct insight into the PHB distribution over the population.