Concentration dependence of the equivalent conductance of isoionic DNA solutions has been studied at different temperatures. The limiting equivalent conductance (lambda infinity) at every temperature investigated has been obtained by extrapolation to the infinite dilution in Kohlraush's plots. At the same time in plots c lambda c versus 1/lambda c (lambda c is equivalent to conductance at the concentration c), corresponding to the linear form of Ostwald's dilution law, the straight lines were obtained. Both lambda infinity and acidity constants (K) have been determined from these plots. The values of lambda infinity by two methods are in well agreement. The average values of lambda infinity were used for energy activation of conductivity calculation, equal to 2,40 +/- 0,05 kcal/mole. The acidity constant of primary phosphoryl groups passes through a maximum near 33 degrees. Equivalent conductance of hydrogen ions calculated by neglecting of macroion's mobility and by using of potentiometric determined concentration (cH+) has been shown to increase with cH+. Unusual behavior of DNA in isoionic solutions is discussed.