The rheological properties of the hyaluronic acid (HA) produced by the cultivation of Streptococcus zooepidemicus ATCC 39920 in synthetic medium at constant pH of 7.0 were determined. Relevant characteristics of the biopolymer as its pureness related to proteins (0.44 mg of protein per gram of HA) and its average molar weight (4.0 x 10(6) Da) were also determined. Experimental data in steady shear (flow curves) have been correlated with the Cross model, which described the apparent viscosity shear rate data well mainly at concentrations higher than 50 mg mL(-1). The concentration dependence of specific viscosity showed two linear regimes that intercept at critical overlap concentration (c*) equal to 4 mg mL(-1). The storage (G') and loss (G '') moduli increasing along the HA concentration and estimates out of the studied range indicate that a crossover frequency decreased with the increasing concentration of HA. The high concentration dependence of G' as well as the deviations of the Cox-Merz rule for most of the HA concentrations indicate the hyperentangled properties for the HA chains, which could be visualized through atomic force microscopy images even at low concentrations as 0.01 mg mL(-1). (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 126-133, 2011