PC-SPES is a herbal mixture used by prostate cancer patients as an alternative form of treatment. Since PC-SPES is derived from eight individual herbs, each with distinct as well as overlapping properties, it is of interest to investigate whether a particular herb in the formulation principally accounts for the biological properties of PC-SPES. We tested the ability of extracts from individual herbs, using amounts estimated to be equivalent to that present in the herbal mixture, to suppress LNCaP cell growth and/or lower PSA expression, in comparison with cells treated with PC-SPES. Cells were incubated with 0, 1, and 5 μl/ml of single herbal extract for 72 h and proliferation/viability was measured by trypan blue exclusion. LNCaP cells treated with 5 μl/ml ethanol extracts of PC-SPES showed a 72-80% reduction in cell growth, and had a similar decrease in cell viability. These results contrasted with cells incubated with 5 μl/ml of individual herbal extract, which suppressed growth in the following order: Dendranthema morifolium Tzvel (85.2% reduction) > Panax pseudo-ginseng (80.9%) > Glycyrrhiza uralensis Fisch (73%) > Rabdosia rubescens Hara (70.8%) > Scutellaria baicalensis Georgi (66.5%) > Ganoderma lucidum Karst (63.5%) > Isatis indigotica Fort (50.0%) > Serenoa repens (14.5%). Analysis of efficacy of individual herbs to control intracellular/secreted PSA levels and the expression of AR and PSA revealed that only Glycyrrhiza uralensis Fisch, Scutellaria baicalensis Georgi and Serenoa repens lowered intracellular and secreted PSA, while the remaining herbs actually increased PSA expression. Also, no uniform response in AR/PSA was observed in individual herb treated cells, contrary to PC-SPES, which elicited a coordinated change in AR/PSA. Lack of concordance between changes in prostate cell growth and prostate specific gene expression makes it unlikely that the activity of a single herb can account for the overall effects of PC-SPES.