Variations of time difference between two-wavelength photoplethysmographic (PPG) signals in various biological conditions was examined and potential of these time shifts for biological analysis was investigated. In this paper a sensor system was made for recording of two-wavelength PPG signals. Then, the signals were recorded in 3 different biological conditions (wakefulness and sleep, rest and run, smoking and not smoking) with participation of 5 individuals at different times. Results showed that there are significant variations in the time difference between different PPG signals (time shifts) in various conditions and presented method had a high potential to biological analysis.