The need for individualized cytostatic therapy is most apparent in cancer patients with disturbance of the liver or renal function and also in patients undergoing combination drug therapy. Bioanalytical studies can provide a rationale for increasing the therapeutic index by optimization of the dose schedule and by site-specific anticancer drug therapy. Analytical methods based on liquid chromatography are discussed for the anthraquinone glycosides, where the high selectivity of reversed-phase liquid chromatography systems permits ready separation from their 14-hydroxy metabolites. The high sensitivity of photometric and fluorimetric detectors permits quantification in the low ng/ml range. The stabilization of alkylating agents such as melphalan in biological samples by reaction with acetylcysteine is discussed. The melphalan-acetylcysteine derivative, after isolation from the biological matrix by reversed-phase liquid chromatography, can be detected fluorimetrically with high sensitivity and selectivity.