Mevastatin arrests the functional maturation of cultured human peripheral blood monocytes. LPS was added to PBMC cultures either at the onset (undifferentiated control), or after 24 h, of cell culture and supernatants were harvested 24 h later in each case. Pre-treatment with γIFN was only applicable to differentiating cells. Mevastatin treatment preserved monocyte responsiveness to LPS in terms of IL-1β release (A) but suppressed IL-1Ra release (B). *, p < 0.05; **, p < 0.01 (brackets indicate groups being compared).