schur q-functions are a family of symmetric functions introduced by schur in his study of projective representations of symmetric groups. they are obtained by putting t = -1 in the hall-littlewood functions associated to the root system of type a. (schur functions are the t = 0 specialization.) this talk concerns symplectic q-functions, which are obtained by putting t = -1 in the hall-littlewood functions associated to the root system of type c. we present several pfaffian formulas for symplectic q-functions similar to those for schur q-functions and give a tableau description. also we discuss some conjectures including the positivity conjecture of structure constants.