We report fluorescence measurements of DNA components performed on the femtosecond time-scale using the fluorescence upconversion technique. Aqueous solutions of thymine (T), thymidine (dT) and thymidine 5'-monophosphate (TMP) were studied in room temperature by excitation at 267 nm and detection at wavelengths between 310 and 380 nm. The fluorescence decays are complex and cannot be described by single exponentials. About 25% of the fluorescence disappears within 150 fs and the remaining part decays more slowly when going from the base through the nucleoside to the nucleotide. The initial fluorescence anisotropy was found to be 0.35+/-0.03 and did not show any drastic change on the examined time interval. (C) 2002 Elsevier Science B.V. All rights reserved.