The response properties and receptive field organization of 106 LSA neurons were investigated in pretrigeminal preparations using moving dark and bright stimuli with particular reference to the dynamic and static structure of receptive fields. About 61percent neurons revealed equal sensitivity to the motions of dark and bright stimuli. A majority of them had an ON-OFF static structure of receptive fields. Nearly 24 percent of cells had higher sensitivity to the motion of dark stimuli in comparison with the bright ones. Their receptive fields constituted the OFF-uniform spatial distribution when tested by stationary flashing lights. No clear-cut correlations were found between the static and dynamic properties of LSA neurons. It was shown that the same region of the receptive field is responsible for the reactions to dark or bright moving stimuli. A group of dark-sensitive neurons (24 percent of the total) was described, some examples of which had no stationary receptive fields at all.