Other nonprescribed medications consumed and not detected on toxicology testing, or other adulterants, might also explain the agranulocytosis. Nevertheless, we advise clinicians to consider the possibility of cocaine use and, specifically, the use of levamisole-adulterated cocaine, in patients with otherwise unexplained fever and agranulocytosis. Prompt urine toxicology testing is essential because levamisole has a short-elimination half-life of 5.6 hours (7) and little of the parent drug (2% to 5%) is detected in urine (8). In addition, cocaine metabolites are detected up to 3.4 days on average after last use (9). Because levamisole is not detected by routine immunoassay toxicology screening tests, other techniques, such as GC/MS, are required.