Surface tensions, gamma, of biological polyelectrolytes in aqueous solutions are studied systematically as possible at the air-water interface by the Wilhelmy method. The polyelectrolytes measured are sodium chondroitin sulfates A (NaCRA) and C (NaCRC), sodium poly-alpha,l-glutamate (NaPGA), poly-l-lysine hydrobromide (PLL . HBr), deoxyribonucleic acid (DNA), lysozyme (LZ), and bovine serum albumin (BSA). Linear-type macroions such as NaCR, NaPGA, PLL . HBr, and DNA have no surface activity in a wide range of polymer concentrations below the critical polymer concentration, m*, and increases as the concentration increases above m*. Surface activity of the undissociated state of macroions is rather high in general. Globule-like macroions such as LZ and BSA show high surface activity at isoelectric point above m* accompanied with orientation of the molecules along the air-water interface. Separation into the hydrophobic and hydrophilic parts at the interface and balancing in their strength are important for appearance of surface activity. Copyright 1998 Academic Press.