A survey of a large sample of Japanese industrial plant personnel is conducted in order to investigate the determinants of effective teamwork. Affinity relationship and multivariate analysis methods were used to identify the underlying determinants of teamwork. The relationships between such determinants for group leaders and their subordinates as a function of group size are analyzed. Teamwork determinants are classified into two categories, namely Task Oriented which relate to group productivity, and People Oriented which relate to group cohesiveness. In general group leaders perceived the latter category of determinants as being necessary for effective teamwork, while their subordinates believed that task oriented determinants were more important.