The amount eaten by humans in spontaneously ingested meals is positively correlated with the number of other people present. This could be due to a social facilitation or may occur as an artifact of a covariation produced by changes in intake occurring over weekends. This possibility was investigated by paying 315 adult humans to maintain 7-day diaries of everything they ingested, when and where they ingested it, and the number of other people present. During weekends, larger meals were ingested, in the presence of more people than during weekdays. However, strong, positive, and significant correlations between meal size and the number of other people present were found separately for meals eaten only during week-days and for those eaten only during weekends. The results suggest that the correlation results from a true social facilitation of eating and that this facilitation is an important determinant of the eating behavior of normal humans.