The primary objective of this trial is to investigate the safety and tolerability of BI 639667 in healthy male subjects following oral administration of single rising doses.

Secondary objectives are the exploration of the pharmacokinetics (PK) including dose proportionality as well as investigation of linearity and pharmacodynamics (PD) of BI 639667 after single dosing and the assessment of the PK/PD relationship.

Inclusion criteria:

1. Healthy male subjects
2. age of 18 to 50 years
3. body mass index (BMI) of 18.5 to 29.9 kg/m2

Exclusion criteria:

1. Any finding in the medical examination (including BP, pulse rate (PR) or ECG) is deviating from normal and judged as clinically relevant by the investigator
2. Repeated measurement of systolic blood pressure greater than 140 mmHg, diastolic blood pressure greater than 90 mmHg, or pulse rate outside the range of 50 to 90 mmHg at screening
3. Any laboratory value outside the reference range that the investigator considers to be of clinical relevance
4. Any evidence of a concomitant disease judged as clinically relevant by the investigator
5. Gastrointestinal, hepatic, renal, respiratory, cardiovascular, metabolic, immunological or hormonal disorders
6. Surgery of the gastrointestinal tract that could interfere with kinetics of the trial medication (except appendectomy and simple hernia repair)
7. Diseases of the central nervous system (such as epilepsy), other neurological disorders or psychiatric disorders