A study of the effects of controversy and concurrence-seeking in cooperative learning groups was conducted with 36 engineering students, in order to clarify the role of controversy by examining oral interaction among group members. Two controversial issues were studied and discussed for five days each: (a) hazardous waste (dispose vs eliminate) and (b) energy production (coal vs nuclear). At the end of each instructional period the students wrote a report, and completed an achievement test and an attitude survey. Trained observers recorded the oral interaction among the group members. Achievement and attitudes were similar for the two conditions, indicating that controversy did not have a negative effect. More of the oral interactions were elaborative in the controversy condition, whereas more were informative in the concurrence-seeking condition.