The coupling of benzenediazonium chloride with benzoylacetone at two different pH values in 1:1 molar ratio gives two different tautomers, PHB and BAB, in that condensation of these dyes with isonicotinic acid hydrazide (INH) yields two different hydrazones PHBH and BABH. Thermal studies (DTA and TG) with spectral analyses (IR and electronic) have provided more information about the structure of PHBH which shows thermochromic behaviour. The d.c. electrical conductivities of these compounds were measured in the temperature range 25-70-degrees-C and were found to show semi-conducting behaviour. The activation energies for conduction were calculated. Valuable results were obtained from the comparison between DELTAE of the azo and hydrazo tautomers, and of the dye and its hydrazone. A graphical method was suggested in order to make a simple comparison between the values of the electrical conductivity exponent.