In the preclinical phase of basic medical education at the Karolinska Institute in Stockholm, Sweden, chemistry extends over 16 weeks and changes were made to the teaching methods during 7 of those weeks--one in organic chemistry and 6 in intermediary metabolism. The number of lectures was reduced and problem-oriented group tasks wee introduced instead which required a higher level of student responsibility for individual learning. Teaching and group tasks were designed to give the students a better understanding of the biochemical processes in their entirety as well as the way these are controlled in the human body. From this base the students will be enabled to discuss and understand physiological, pathological and medical phenomena. Experience and results show that student performance in examinations improved significantly, that students acquired a better understanding and a more comprehensive grasp of the subject, and a noticeably more positive interest in medical chemistry. They remember approximately 60% more a few years after completing the course than do students who have been instructed in a more traditional manner, and although the load of the teachers has increased by some 20% in respect of scheduled time, the instructors have gained in improved student contact and a wider knowledge of their subjects. The results have remained the same for each course since the change was introduced in 1977. Due to new admission criteria, more students now have less knowledge of mathematics and chemistry, and more students have social circumstances that make independent studies more attractive (family obligations and financial obligations).(ABSTRACT TRUNCATED AT 250 WORDS)