Dilute solution properties of copolymers of N-vinylformamide (NVF) with sodium 3-acrylamido-3-methylbutanoate (NaAMBA), sodium 2-acrylamido-2-methylpropanesulfonate (NaAMPS), and sodium acrylate (NaA) of known molecular weight and compositions have been studied in regard to added cosolutes, pH, and temperature. Phase separation studies have also been performed. All copolymers display typical polyelectrolyte behavior as observed by a reduction in viscosity in the presence of added electrolytes. Copolymers from all three series display losses of viscosity in the presence of urea at pH = 8.5. With the exception of a few copolymers of NVF with NaA (AAVF-100, -82, and -49), all copolymers investigated exhibit no phase separation in the presence of calcium chloride at 25 degrees C. Copolymers of NVF with NaAMPS (PSVF series) are soluble throughout the pH range investigated, while most copolymers from the BAVF and AAVF series phase separate as the pH of the aqueous medium is lowered. At low pH, phase separation at the lower critical solution temperature is observed for the BAVF series. Conversely, the phase separation of the AAVF copolymers is representative of an upper critical solution temperature and is affected by the presence of added cosolutes such as sodium chloride and urea.