The potential of a DNA content assay, PicoGreen, for use in 3D bioengineered constructs was examined. The assay was tested on ATDC5 cells in situ during culture in typical tissue engineering 3D constructs. Comparisons of cell standards from cell lines and primary cells to lambdaDNA standards was also conducted. An effective working range of the assay within 3D constructs was shown up to 2.5 x 10(5) cells ml(-1). From significant variation found in DNA content between cell lines and primary cells, it was concluded that the most accurate standard to use for the assay was from the cell type being examined.