Contrary to the curricular reform practices of the past, today the focus of science education reform is on new classroom routines. The central role of teachers in what transpires in science classrooms has long been recognized and constructivist teaching practices are promoted throughout the world. Educators and educational reformists are working on ways to gain insight into teachers' professional actions to help them improve their instructional practices (Czerniak, Lumpe and Haney, 1999, Schneider, Krajcik and Blumenfeld, 2005) and to bring about the changes intended in the new science curricula.Various factors related to teachers' beliefs and perceptions are identified in the literature as shaping what teachers do in the classroom. Researchers in the field also give some characteristics of teachers i.e. age, sex, years and level of experience, the educational background, and participation in in-service training that may possibly influence what they do in the classroom.This study reports the findings of two researches carried out in 2002 and 2004 with the participation of 1023 biology teachers working in 28 Turkish cities. The first study intended to identify the influence of teacher characteristics such as age, sex, years of teaching experience and attendance at in-service training programs on the way biology is taught. The follow-up study focused on the in-service training needs of the biology teachers and searched for a significant relationship between teachers' age, sex, teaching experience and previous attendance at in-service training activities and their in-service training needs.Stratified random and cluster random sampling strategies were followed and survey questionnaires were applied in both studies. The data collected from randomly selected teachers were then analyzed through descriptive and inferential statistics, and qualitative data analysis techniques.The underlying reasons of the differences observed in teaching biology in relation to the different teacher characteristics in the first study were thought to originate from unequal representation of male and female teachers in the sample, the way these teachers were trained as teacher candidates, and teachers' possible resistance to changing the way they teach. The last finding also highlighted the inefficiency of the in-service training programs for helping teachers to change their beliefs and practices. Since the findings of the second study also pointed out to the differences between participant teachers' in-service training needs and experiences related to their age, sex, and teaching experience, researcher calls attention to an emerging need for a new agenda that promotes effective and continuous training of biology teachers in Turkey. Although the inferences made were specific to the Turkish context and many of the specific issues may be of purely local interest, the findings of the studies urge us to consider the need to examine teachers' continuous training as a means to improve instructional practices for science education, not just in Turkey but also in other countries. Czerniak, C.M., Lumpe, A.T. and Haney, J.J. (1999). Science teachers' beliefs and intentions to implement thematic units. Journal of Science Teacher Education, 10(2), 123-145. Schneider, R.M., Krajcik, J. & Blumenfeld, P. (2005). Enacting Reform-Based Science Materials: The Range of Teacher Enactments in Reform Classrooms. Journal of Research in Science Teaching, 42(3), 283-312