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The evolution of fractionally quantised states has been studied in a GaAsGaAlAs heterojunction as a function of electron concentration at very low temperatures using magnetic fields up to 16T. The electron concentration was progressively increased by the use of the persistent photoconductivity effect, and it was found that the fractionally quantised states at occupancies of 53, 75and43became much more pronounced. The 43state gave only a weak resistivity minimum and no Hall plateau at the highest concentration studied (4.6×1011cm−2), in contrast to the 53state, for which a wide Hall plateau and a deep resistivity minimum were observed.