Both the longest tissue half-time (T1/2max) and the maximum allowable pressure gradient (deltaP) define the safe rate of decompression (DR) after saturation expositions. The mathematical relation between them (DR = -k x deltaP, where: k = ln(2)/(T1/2max)) suggests that experimentally established decompression rate can be hypothetically described by the infinite number of T1/2max and deltaP combinations. The observed number of decompression sickness after saturation decompressions forced to change those parameters subsequently and finally led to values far outside physiological range. Therefore the aim of this study was to compare values of the longest tissue half-time of nitrogen desaturation from diver's body published since 1908 in order to present the evolution of opinions concerning desaturation process. Non-physiological values of T1/2max (from 75 to 1280 minutes) have been published during historical evolution of decompression tables and systems. The currently accepted values of T1/2max (in the range of 320-480 minutes) for saturation and non-saturation air and nitrox divings and hypobaric decompressions, still need to be precised. The discrepancy between T1/2max values obtained using isobaric decompression method and decompressions after diving indicates different physiological phenomena during nitrogen elimination in both methods.