  We investigate variability of optical and near-infrared light curves of the
X-ray binary GX 339-4 on a timescale of days. We use the data in four filters
from six intervals corresponding to the soft state and from four intervals
corresponding to the quiescent state. In the soft state, we find prominent
oscillations with the average period P = 1.772 $\pm$ 0.003 d, which is offset
from the measured orbital period of the system by 0.7 per cent. We suggest that
the measured periodicity originates from the superhumps. In line with this
interpretation we find no periodicity in the quiescent state. The obtained
period excess $\epsilon$ is below typical values found for cataclysmic
variables for the same mass ratio of the binary. We discuss implications of
this finding in the context of the superhump theory.
