We have studied the low-temperature photoluminescence of high-mobility two-dimensional hole gases in GaAs quantum wells in magnetic fields up to 50 T. We have observed both spin states of the neutral (X-0) and of the singlet state of the positively charged exciton (X-), allowing us to determine their g-factors and the binding energy of X-. We find that the g-factor of the X is larger than that of X-0 by a factor of 1.6. In very high fields. we expect the low-energy spin-state of X- to be bound only because of the Zeeman interaction. (C) 2002 Elsevier Science B.V. All rights reserved.