This book is based on a very simple idea, investigating a patient for reaching an accurate and precise workable diagnosis with minimum expenditure of finances and energies and not for the sake of investigations.   The investigations and tests are the tool to reach an accurate diagnosis. These are required to confirm a diagnosis made after adequate history and clinical examination. These should give maximum information with minimum discomfort to the patient. We should use these to the advantage of the patient very precisely and economically.   We have tried to discuss the tests in simple language. The efficiency, the indications, the advantages and disadvantages of the tests have been discussed in a hope that unwanted tests may not be asked and patient's money, time and trouble may be spared. The investigations should be cost effective.