Energy gaps have been measured for the ferromagnetic quantum Hall effect states at and 3 in heterojunctions as a function of Zeeman energy, which is reduced to zero by applying hydrostatic pressures of up to 20 kbar. At large Zeeman energy the gaps are consistent with spin-wave excitations. For a low-density sample the gap at decreases with increasing pressure and reaches a minimum when the g-factor vanishes. At small Zeeman energy the excitation appears to consist of a large number of reversed spins and may be interpreted as a skyrmion. The data also suggest that skyrmionic excitations take place at . The width of the minimum at is found to decrease as the g-factor is reduced in a similar way for all samples.