Relationships among cytological features, doubling time, S-phase percentage, expression of myc-family oncogenes, DNA ploidy and biochemical properties were studied in thirteen small cell lung cancer cell lines. Six cell lines that grew slowly (average doubling time 99 h) and had lower S-phase percentages (average 32%) showed inconspicuous nucleoli (average area of 1.5 microns 2), and the remaining seven cell lines that grew quickly (average doubling time 45 h) and had higher S-phase percentages (average 44%) showed large and prominent nucleoli (average area of 6.1 microns 2). DNA index value obtained from flow cytometric DNA histograms showed that all cell lines except for H-69 cell line displayed aneuploidy. Ribbon-like cell arrangements were observed in the 7 cell lines that grew quickly, and in 1 cell line that grew slowly. Biochemically, six slow-growing cell lines and four fast-growing cell lines showed high levels of aromatic L-amino acid decarboxylase activity, while in the remaining three fast-growing cell lines its level was low. A high level of c-myc or N-myc oncogene expression was observed in all 7 cell lines that grew quickly, but not in any of the 6 cell lines that grew slowly. It appears that small cell lung cancer cell lines that grow quickly can be expected to have large nucleoli and ribbon-like cell arrangements and to express high levels of myc-family oncogenes, and that nucleolar size is a good indicator for growth characteristics.