Investigators are regarded as central to the concept of clinical trials. Apart from bearing scientific responsibility, they will be confronted with a great number of ethical dilemma's concerning, amongst others, the justification and design of the trial, subject selection and informed consent, and presentation of the trial results. The ethical principles of biomedical research should be observed in accordance with a consistent moral code. The moral code of Good Clinical Practice (GCP) was developed in order to rule out inconsistencies. The principal tenets are that clinical trials should be good science, verifiable, monitored, well documented, and that they comply with the highest ethical standards. The principles of GCP are the protection of the rights of human subjects, integrity and reproducibility of data, and transparency of conduct.