Atherosclerosis has highly important chronic inflammatory aspects. We investigated anti-inflammatory effects upon initiating insulin therapy by measuring serum high-sensitivity C-reactive protein (hsCRP) and plasma fibrinogen and serum monocyte chemoattractant protein (MCP)-1in patients with poorly controlled type 2 diabetes. In 18 inpatients with type 2 diabetes, we measured serum hsCRP, plasma fibrinogen, serum MCP-1, body weight (BW), girth, and fasting plasma glucose (FPG) before and 2 weeks (14.0 +/- 2.5 days) after initiation of insulin therapy. Daily insulin doses (in units) were approximately 0.2 x BW (in kilograms). Various changes (ratio) were calculated as the ratio of the value during treatment to the pretreatment value. Significant decreases occurred for log(10) hsCRP and FPG (-0.025 +/- 0.557 mg/L, 215 +/- 64.3 mg/dL v -0.213 +/- 0.571 mg/L, 129.8 +/- 32.1 mg/dL; P =.0121, and P =.00002, respectively). This was particularly true for log(10) hsCRP in patients whose BW was unchanged or increased between measurement (P =.0050). There were no significant differences between pretreatment and treatment values for fibrinogen and MCP-1. However, MCP-1 decreased significantly in the group with high-value in the first time point (MCP-1 > 250 pg/mL, n = 9; P =.0224) compared with the low-value group (MCP-1 < 250 pg/mL, n = 9; P =.3164). No significant correlation was found between hsCRP ratio and fibrinogen ratio, MCP-1 ratio, BW ratio, waist girth ratio, or FPG ratio. In conclusion, newly initiated insulin therapy in patients with poorly controlled type 2 diabetes decreased serum hsCRP. The decrease in hsCRP may have resulted largely from anti-inflammatory effects of insulin.