Research of the biology component of the Teacher Assessment Project (BioTAP) was conducted to explore the feasibility of using performance-based assessments to evaluate high school biology teachers. Three modes of performance-based assessment were employed: portfolios, portfolio-based simulations, and simulation exercises. Fifteen high school biology teachers completed 11 assessment activities during the 1988-89 academic year and the summer of 1989. Using a holistic scoring procedure and group deliberation, the performances of the teachers were rated. This paper reviews the design and administration of the assessment activities, reports on the rating process, the results of the rating, and the teachers' and research teams' reactions to performance-based assessments. The personnel, portfolio, the assessment center, rating, findings, conclusions, and implications are topics of discussion. A copy of the rating form and 24 references are appended. (KR)