Whooping cough continues to be a major childhood disease in parts of West Germany. At age six, more than one third of the children in our area have had pertussis according to parental information, whereas only 12% received a specific vaccination. During a four-year period from 1984 to 1987, a total of 2,881 clinically diagnosed cases of whooping cough were investigated. The children had a mean age of 4.1 years, 11% of all patients were younger than one year and 6% of the patients were adults with a mean age of 35.8 years. No sex difference was observed in children (less than 20 years) with clinically overt whooping cough. The seasonal distribution showed that whooping cough was present throughout the year, peaking in early winter. In relation to clinical symptoms, the isolation rate of Bordetella pertussis or Bordetella parapertussis from nasopharyngeal swabs continuously decreased with the duration of paroxysms, starting with 56% positive swabs on day 1. Titers (greater than or equal to 1:100) of IgA-antibodies to B. pertussis antigens increased with the duration of paroxysmal coughing. B. pertussis, however, was also isolated from 152 of 964 patients without the clinical signs of whooping cough. IgA-antibodies were also found in 522 patients with non-typical respiratory symptoms, but not in healthy blood donors. Children with clinically diagnosed whooping cough were compared to a group of children showing the symptoms but without any clinical or laboratory signs of whooping cough. We can assume from our data that the incidence and duration of non-paroxysmal coughing, the nocturnal increase in coughing, fever, auscultatory findings and a contact anamnesis occurred with a similar frequency in the whooping cough group and the control group. Apart from the typical paroxysmal fits, whooping and vomiting were found significantly more often in the pertussis group. At least 19% of patients with a recent infection with B. pertussis, however, were not diagnosed by clinical symptoms. The leukocyte count differed only marginally between the three groups and was of no great diagnostic value. A relative lymphocytosis, however, was found significantly more often in whooping cough patients and in patients with laboratory-diagnosed infection with B. pertussis. Our study indicates that part of the symptomatology and some laboratory findings in whooping cough patients in endemic areas of West Germany may differ from the classical form of the disease. Furthermore, our data stress the importance of an accurate procedure in diagnosing B. pertussis infection, and this can be facilitated by a combination of bacteriological and serological tests.