Fluorescence emission spectra from anthracycline-treated cells suspended in buffer have been studied. The kinetics of uptake and the nuclear concentration of anthracyclines in human lymphocytes have thus been determined using the fluorescence properties of these drugs. Four anthracyclines have been used: adriamycin (ADR), 4'-O-tetrahydropyranyl-adriamycin (THP-ADR), carminomycin (CAR) and aclacinomycin A (ACM). We have shown that no quenching of the drug fluorescence is obtained through interaction of the drugs with the various components of the cell except the nucleus. No quenching is observed with cells lacking nucleus such as platelets and erythrocytes. Quenching of drug fluorescence occurs when drugs intercalate between base pairs of DNA only. This allows rapid determination of the amount of drug intercalated between nuclear base pairs in the steady state. We have thus estimated that one molecule of drug can bind for every 10, 8.3, 10 and 6.7 DNA base pairs in the case of ADR, THP-ADR, ACM and CAR, respectively. The kinetics of drug incorporation into the nucleus, once the cells have been solubilized with triton X-100, is very fast for the four drugs. However, the kinetics of drug uptake by the intacts cells strongly depends on the nature of the drug. When 10(9) cells/l are incubated with 1 microM drug, 50% of the final nuclear concentration is reached within 97 min, 3.2 min, 3.0 min and 1.2 min in the case of ADR, THP-ADR, CAR and ACM, respectively. The kinetics directly correlates with the polarity of the molecule.