A small biotechnology company in La Jolla, Calif., is the first firm to win permission from the U.S. Food and Drug Administration to market a product that many claim will open a new chapter in laboratory medicine.

Hybritech Inc.'s Tandem IgE Kit is a highly sensitive device intended to help physicians diagnose and monitor human allergies. The FDA's approval, industry sources say, establishes Hybritech as the current leader in a field traditionally dominated by large biomedical companies such as Warner-Lambert, Abbott Laboratories, and Johnson & Johnson.

The Tandem IgE Kit relies on the production of monoclonal antibodies -- pure antibody molecules manufactured outside the body, which provide clinicians with greater sensitivity and specificity in detecting substances in the blood. Researchers predict monoclonal antibodies will ultimately be used in the diagnosis and treatment of cancer and viral infections.

Hybritech plans to develop 15 to 20 individual kits to help diagnose a variety of diseases, including hepatitis and certain forms of cancer. Several other companies are also at work on kits using monoclonal antibodies.

The market for such products may reach $485 million in the United States and as high as $870 million worldwide by 1985, estimates Henry Weinert, president of Boston Biomedical Consultants Inc. The market for Hybritech's IgE Kit alone is about $6 million to $8 million worldwide, Weinert adds.