Cyclin D1 is a key cell cycle regulator protein with demonstrated oncogenenic activity in a variety of malignancies. Overexpression of Cyclin D1 protein has been observed in many types of tumors. We hypothesized that Cyclin D1 might be an important determinant of the sensitivity of neuroblastomas to cisplatin. Cyclin D1, D2 and D3, and Cdk4, Cdk6 and Rb protein, and Cyclin D1 mRNA expression were measured in primary patient-derived neuroblastoma cell lines. Cell cycle distribution was examined using flow cytometry. A modified MTT assay was used to determine the sensitivity of the cell lines to cisplatin. All 14 cell lines expressed Cyclin D1 protein to a variable extent (0.22-1.47 normalized to actin protein expression). All cell lines expressed Cyclin D2 and D3. There was no relationship between expression of Cyclin D1 and expression of Cyclin D2 or D3 (p>0.05 and R2<0.2 for both). All cell lines expressed Cdk4 and Cdk6 protein. In addition, Rb and two related proteins, p105 and p130, were detected in all the cell lines. The mean cisplatin IC50 was 19.2 microM (range 0.6-40 microM). We conclude that there was no correlation between the amount of Cyclin D1 expressed and the cisplatin IC50. Our results do not support the hypothesis that Cyclin D1 expression is significantly related to cisplatin resistance.