We report here on the detection and fluorescence lifetime measurement of single Rhodamine- 110 molecules in a flowing, aqueous sample stream. Time-correlated photon counting (TCPC) used in combination with pulsed excitation allows for the detection, in the presence of significant prompt Raman and Rayleigh background, of photon bursts due to single fluorescent molecules passing through a small detection volume (approximately 1 pL). The fluorescence lifetime of a detected molecule is estimated from the decay curve complied from photon arrival times in the burst.