The firm's investigation for Complaint for Fluorescein USP Lot is inadequate in that the firm did not evaluate the returned material as required by the firm's written procedure. The complaint alleged that the endotoxin level exceeded the customer's acceptable limit. The investigation failed to include notification to the laboratory for the release of the lot for an investigation at the laboratory. Additionally, the firm did not conduct a review of the manufacturing records and conducted no further testing at the time the material was returned. The Fluorescein USP lot was returned to the firm and then stored for several months and subsequently distributed to other customers after repeating the assay, moisture, and endotoxin testing.