The pathogenesis of aplastic anemia from chloramphenicol (CAP) remains uncertain. Recent observations suggest that metabolites of CAP generated by intestinal bacteria may play an important role in mediating hematotoxicity from the drug. Thus, it is possible that once in circulation and after passage through the liver, some CAP metabolites may gain access to the marrow causing hematotoxicity. Based on this possibility, we have studied the stability of CAP and the three cytotoxic analogues dehydrochloramphenicol (DH-CAP), nitrophenylaminopropanedione (NPAP) and nitroso-chloramphenicol (NO-CAP) in human blood and liver. Determination of these compounds was accomplished by using a high-performance liquid chromatography system uniquely suited for their separation and detection. Several methods for deproteinization were utilized in order to ensure a full quantitative extraction of the drugs. At zero time, a 100% recovery of CAP, DH-CAP and NPAP was reached with acetonitrile (1 vol/3 vol); whereas NO-CAP was slightly or not detectable with all methods. Incubation of CAP and analogues with blood or liver at 37 degrees C for up to 30 min showed the following: CAP was stable in both tissues with full recovery; DH-CAP was stable for 5 min, then gradually decreased reaching 50 or 70% of the initial amount after 30 min of incubation with blood and liver, respectively; NPAP decreased at a faster rate than DH-CAP, and NO-CAP completely disappeared. The data suggest that if and when formed in the body, DH-CAP and NPAP may stay in the circulation long enough to reach the marrow and interact with its cellular components.