The concept of autoimmune aetiology of some cases of chronic urticaria (CU) has been supported by several observation including wheal-and-flare reaction induced by intradermal injection of autologous serum as well as association with other autoimmune diseases, in particular Hashimoto's thyroiditis (HT). It is known that activated platelets may actively participate in immune-inflammatory processes. Therefore, we assessed whether autoimmune phenomenon associated with CU influence the systemic platelet activity measured by circulating level of platelet factor 4 (PF-4). Plasma level of PF-4 was analysed using enzyme-linked immunosorbent assay in twelve women with strong positive response to autologous serum skin test (ASST) suffering from CU, twelve female patients with strong positive ASST suffering from both CU and untreated, HT as well as sixteen healthy women. All the subjects were clinically and biochemically euthyroid. There were no statistically significant differences between the CU patients with or without euthyroid HT and plasma PF-4 level in healthy controls. In patients with both CU and thyroiditis, plasma level of PF-4 did not correlate significantly with the level of antibodies against thyroperoxidase. It seems that circulating level of the platelet-derived chemokine is not increased in CU patients with positive response to ASST, regardless the occurrence of euthyroid HT.