People sometimes report that their relatives who have been diagnosed with Parkinson's disease (PD) have a unique smell. A previous study has demonstrated that PD patients do have smell that is different from that of healthy people. Sniffer dogs have long been used to identify criminals, and recently been used to identify subject with cancer. The investigators hypothesized that sniffer dogs may be able to identify PD patients.

Parkinson's Disease is a neurodegeneration disorder that affects the life of millions of people worldwide. There are multiple drugs available now that can modify the process of the disease. Making a timely and correct diagnosis of PD is still a great challenge in many cases even for specialists. Correct diagnosis is fundamental to the appropriate administration of medicines. To help clinicians to quickly and correctly make a diagnosis, the investigators aim to use sniffer dogs to identify PD patients from clearly non-PD subjects. After more than one-year training of the dogs, the investigators found that it is feasible to use dogs to identify PD patients from non-PD subjects. Now the investigators are trying to estimate the sensitivity and specificity of sniffer dogs in identifying PD patients from non-PD subjects.

In this multicenter study, the clinicians and their assistants will collect samples and send to the study center. One researcher alone will put seven plastic bags containing matched samples (one PD sample and six non-PD samples) on a table and take notes, then relabel them with random numbers and take notes again, and keep them in a confidential place till the study is completed. Another researcher will take over the relabeled samples and put them into different tanks and take notes. Thus, both the experimenter who helps to place the samples into tanks and the dog handler will not know the nature of the samples. Test results will be compared with the notes of the blind-setter after all the experiments have been performed. The sensitivity and specificity of identification will be calculated. The study aims to test the hypothesis that the diagnostic sensitivity of sniffer dogs in identifying PD patients from non-PD subjects is over 90%.

Inclusion Criteria:

• Clinically established PD patients
• Clearly non-PD subjects will be recruited as controls

Exclusion Criteria:

• subjects with tremor or decrease of olfactory power or with rapid eye movement sleep behavior, obvious constipation, and depression.
• subjects who are taking antipsychotics.
• subjects with incomplete data.

PD patients and other subjects in clinics