A series of random copolymers of N-isopropylacrylamide (NIPAM) and sodium 2-acrylamido-2-methyl-1-propanesulphonate (AMPS) was synthesized by free-radical copolymerization. The content of AMPS in the copolymers ranged from 1.1 to 9.6 mol %. The lower critical-solution temperature (LCST) of copolymers in water increased strongly with an increasing content of AMPS. The influence of polymer concentration on the LCST of the copolymers was studied. For the copolymers with a higher AMPS content, the LCST decreased faster with an increasing concentration than for copolymers with a low content of AMPS. For a copolymer containing 1.1 mol % of AMPS the LCST dropped by about 3 degreesC when the concentration increased from 1 to 10 g/L, whereas for a copolymer containing 9.6 mol % of AMPS the LCST dropped by about 10 degreesC in the concentration range from 2 to 10 g/L. It was observed that the ionic strength of the aqueous polymer solution very strongly influences the LCST. This effect was most visible for the copolymer with the highest content of AMPS (9.6 mol %) for which an increase in the ionic strength from 0.2 to 2.0 resulted in a decrease in the LCST by about 27 degreesC (from 55 to 28 degreesC), whereas for the copolymer containing 1.1 mol % of AMPS the LCST decreased only by about 6 degreesC (from 37 to 31 degreesC) when the ionic strength increased from 0.005 to 0.3. The reactivity ratios for the AMPS and NIPAM monomer pairs were determined using different methods. The values of r(AMPS) and r(NIPAM) obtained were 11.0-11.6 and 2.1-2.4, respectively.