The primary aim of this study was to determine serum Hsp70 concentrations in HELLP syndrome. We measured also the serum concentrations of three acute phase proteins: C-reactive protein (CRP), alpha(2)-macroglobulin (AMG) and alpha(2)-HS glycoprotein (AHSG). Ten severe preeclamptic patients with HELLP syndrome, 20 severe preeclamptic patients without HELLP syndrome and 20 normotensive, healthy pregnant women were included in this case-control study. Serum concentrations of Hsp70, CRP, AMG and AHSG were measured using an enzyme-linked immunosorbent assay (Hsp70), particle-enhanced immunoturbidimetric assay (CRP) and radial immunodiffusion (AMG, AHSG). The serum Hsp70 and CRP concentrations were significantly higher, whereas the serum AHSG concentration was significantly lower in the HELLP group (H) than the severe preeclamptic (P) and control (C) groups (median (25-75 percentile); Hsp70: 2.02 ng/ml (0.76-2.23) (H) versus 0.54 ng/ml (0.47-0.79) (P), p<0.01, and 0.30 ng/ml (0.27-0.33) (C), p<0.001; CRP: 43.9 mg/l (27.1-84.5) (H) versus 6.5 mg/l (2.7-10.7) (P), p<0.001, and 2.5 mg/l (1.1-6.7) (C), p<0.001; AHSG: 588 microg/ml (492-660) (H) versus 654 microg/ml (576-768) (P), p<0.05, and 738 microg/ml (666-804) (C), p<0.01, respectively). The serum AMG concentration did not differ between the study groups. In the HELLP group, there was a statistically significant negative correlation between serum Hsp70 concentration and platelet count (Spearman R=-0.69, p=0.026). In conclusion, serum Hsp70 and CRP concentrations are increased, whereas serum AHSG concentration is decreased, in HELLP syndrome. The maternal systemic inflammation seems to be more pronounced in HELLP syndrome than preeclampsia without HELLP syndrome, as suggested by the alterations in serum CRP and AHSG levels. However, it requires further investigation to determine whether these changes are causes or consequences of the disease.