1 All About Pet Birds.- 1.1 Bird Keeping as an Increasingly Popular Pastime.- 1.1.1 Reasons for Keeping Pet Birds.- 1.1.2 Number of Pet Animals in the Netherlands in 1984.- 1.1.3 Bird Breeders in the Netherlands in 1984.- 1.1.4 Hygiene Among Bird Keepers.- 1.2 Birds as a Source of Pollution.- 1.2.1 Introduction.- 1.2.2 What Can Go Wrong in Caring for Pet Birds?.- 1.2.3 Contribution of Pet Birds to Biological Pollution.- 1.3 Infectious Diseases of Pet Birds That Can Be Transmitted.- 1.3.1 Introduction.- 1.3.2 Parrot Disease (Psittacosis).- 1.3.3 Newcastle Disease Virus Conjunctivitis.- 1.3.4 Inflammation of the Stomach and Intestine Due to Salmonella typhimurium.- 1.3.5 Enteritis Caused by Yersiniae.- 1.3.6 Pasteurellosis.- 1.3.7 Streptococcus and Staphylococcus Skin Infections.- 1.3.8 Erysipeloid.- 1.3.9 Mould Infections.- 1.3.10 Toxoplasmosis.- 1.3.11 Mycoplasma Pneumoniae.- 1.3.12 Mycobacterium Avium.- 1.3.13 Arbovirus Encephalitis.- 1.4 Allergic Diseases That Can Be Caused by Pet Birds.- 1.4.1 Introduction.- 1.4.2 Allergic Rhinitis and Nasal Polyps.- 1.4.3 Allergic Asthma.- 1.4.4 Allergic Alveolitis.- 1.4.5 Granulomas and Irreversible Lung Fibrosis.- 2 Survey of Patients in General Practice.- 2.1 Introduction.- 2.2 Methods.- 2.3 Results.- 2.3.1 Distribution of Risk Factors Among the General Practice Population.- 2.3.2 Mortality Before Age 60.- 2.3.3 Malignant Tumour Incidence.- 2.3.4 Nasal Polyps.- 2.3.5 Problems of Pregnancy.- 2.3.6 Infertility.- 2.3.7 Further Statistical Tests.- 2.4 Discussion.- 3 Hospital Case-Control Study of Lung Cancer and Bird Keeping.- 3.1 Introduction.- 3.2 Methods.- 3.3 Results.- 3.4 Discussion.- 4 Dust Measurement Study.- 4.1 Introduction.- 4.2 Methods.- 4.3 Results.- 4.4 Discussion.- 5 Other Evidence on Bird Keeping and Lung Cancer.- 6 Discussion of the Relationship Between Bird Keeping and Lung Cancer.- 6.1 Introduction.- 6.2 Mechanisms by Which Bird Keeping May Cause Lung Cancer.- 6.2.1 Bioaerosol-Related Allergic and Infectious Diseases.- 6.2.2 Biological Factors Spread by Birds and Their Possible Relationship to Tumour Development.- 6.2.3 Local Immune Deficiency Syndrome.- 6.3 Causes of Lung Cancer and their Relative Importance.- 6.3.1 Smoking.- 6.3.2 Occupation.- 6.3.3 Nutrition.- 6.3.4 Pet Birds.- 6.4 Conclusions and Recommendations for Further Research.- Appendix A Interpreting Data From Epidemiological Studies.- Appendix B Some Investigative Methods.- Appendix C Case Histories of the 22 Couples with Infertility Tests in the General Practice Survey.- Appendix D Steps to Prevent the Formation of Bioaerosols from Pet Birds.- References.