Introduction: The integration of pharmacogenetic testing into routine care will, in part, depend upon the patients’ and physicians’ acceptance of these tests. Empirical data regarding patients’ and physicians’ views on pharmacogenetic testing are lacking. Objectives: To explore patients’ and physicians’ perspectives on the potential implications of pharmacogenetic testing, particularly focusing on asthma, and to analyze the possible determinants of their expectations, hopes and fears. Methods: We conducted telephone interviews with patients with asthma or chronic obstructive pulmonary disease taking part in a larger pharmacogenetic study, in addition to general practitioners (GPs) from a different region in Germany. A total of 328 patients and 378 GPs were invited to participate. Determinants of their attitudes toward pharmacogenetic testing were assessed using logistic regression analysis. Results: Informed consent to participate in this study was given by 196 patients (60%) and 106 GPs (28%). Most patients (96%) and physicians (52%) appreciated the availability of pharmacogenetic tests for a disease such as asthma. Approximately a third of the patients worried about potential unfavorable test results (35%) and violation of privacy (36%). Female patients were more likely to have a fearful attitude (odds ratio [OR] = 2.85; 95% confidence interval [CI] = 1.58–5.12). Younger patients were generally more likely to be hopeful about the usefulness of pharmacogenetic testing (OR = 2.12; CI = 1.01–4.46). The GPs’ concerns were mainly related to the possibility that patients might either be put under pressure to be tested (72%) or be disadvantaged at private health insurance agencies (61%). The nature of the responsible institution, the clarity of the research aim and explicit informed consent from patients influenced a physicians’ decision regarding whether to support a pharmacogenetic study. Conclusion: The concerns of patients and GPs differ somewhat with respect to negative psychosocial consequences, discrimination or violation of privacy. Development of information for physicians and patients would be helpful in preventing unrealistic fears or hopes.