Using thermal denaturation and fluorescence spectroscopy, we have investigated the interaction of antitumor antibiotic, daunomycin, with calf thymus histone H(1) under several ionic strengths. The results show that daunomycin binds to histone H(1) and increases its melting temperature. Increasing ionic strength elevates this effect. Fluorescence emission data show that the interaction of daunomycin with histone H(1) decreases the emission intensity at 325 nm and induces hyperchromicity in the emission spectrum of the drug. The results suggest that histone H(1) can be considered as a new target for drug action at the chromatin level.