Pleasant weather conditions (i.e., sunshine) favor positive social relationships and improve mood. However, the effect of sunshine on spontaneous helping still remains in question. In a field experiment, male and female confederates accidentally dropped a glove on the ground while walking in pedestrian streets. The confederate continued walking, apparently unaware of his/her loss. The experiment was conducted on predominantly cloudy or predominantly sunny days, but precaution was taken to control for the temperature and not to solicit participants when it rained. Passers-by helped the confederates more favorably on the sunnier days. Positive mood induced by sun may explain such results