This aim of this study was to analyze the content of students' verbal interactions within a problem-based learning context in biology. This was achieved through the qualitative analysis of the verbal protocols of three groups of two clases of ninth-grade female students (average/high ability, high/high ability, and average/average ability). The three groups were audio and video taped as they worked collaboratively in the problem-based learning environment to solve a problem case created by another group of students. Data were transcribed and analyzed using the idea unit approach. Overall, these groups were successful at negotiating roles and materials to be used to help them solve the problem case. Members in all three groups alternated in terms of researching and obtaining information, reading materials, and note-taking. Few disagreements were found, and when they did occur, they were often quickly resolved. When the students were of equal academic ability, the division of power was shared, but in the average/high ability group, the higher ability student tended to dominate the conversation and assume a more authoritative role. The implications of these findings, particularly of the inequality in participation among students of differing academic abilities, for instruction are discussed. (Contains 2 tables and 12 references.) (SLD)