The first step in Rosenhan's experiment was for him and his pseudopatients to have clinical interviews and report their one symptom- they were hearing voices.
Each pseudopatient got diagnosed with a mental disorder 11 out of 12 got diagnosed with schizophrenia but one got diagnosed with manic depression (bipolar) this was at a private hospital.
Once all the pseudopatients were admitted to the hospital they began to act normal and stopped reporting hearing voices
While in the hospital all the pseudopatients took a notepad and pen. They then recorded everything they heard while in the hospital (unstructured observation) covertly unless they were found out by any staff then they were to continue their observation overtly.
There were also structured observations carried out in 3 of the hospitals where they noted down how many patients voiced suspicions and how much time the staff spent with patients. In four of the hospitals, they asked "Pardon me, Mr [or Dr or Mrs] X, could you tell me when I will be eligible for grounds privileges?” or “ when I will be presented at the staff meeting?” or “.when I am likely to be discharged?" And noted their reply.
All the pseudopatients were then released though the times it took to release said pseudopatients varied it took 7-52 days for them to be released (the mean being 19 days) and none of the staff recognised that any of them were healthy all were released with schizophrenia in remission bar one who was released with schizophrenia still on their medical record.