The purpose of this study was to determine whether erythrocyte hemolysis occurs during a mountain ascent over snow and ice to 3285 meters. Data were collected from six experienced recreational mountaineers, 2 females and 4 males, who participated in a six-day ice climbing seminar and peak ascent in the North Cascades mountain range of the United States. Blood samples were collected from an antecubital vein at sea level (S1), in a base camp at 1515 m prior to the summit ascent (S2), on the summit at 3285 m after 6.5 hours of climbing (S3), at base camp immediately after the descent (S4), and at sea level following a trail descent from the base camp (S5). Whole blood samples were chilled and analyzed for complete blood count including hemoglobin (Hb) concentration, hematocrit (Hct), and white blood cell count (WBC). Serum was frozen and later analyzed for serum haptoglobin (Hapt). No significant changes were found for Hct and Hb among the samples. Mean (+/- SEM) Hapt values were 125 (+/- 28), 113 (+/- 25), 100 (+/- 18), 103 (+/- 32), and 109 (+/- 23) mg.dl-1 for S1 through S5, respectively. No significant differences were found among the Hapt values. Plasma volume changes (% PVC) were calculated from Hct and Hb. Mean estimated % PVC were -4.16 (+/- 1.55), -2.54 (+/- 3.93), 7.46 (+/- 4.86), and 4.80 (+/- 3.49) percent between S1 and S2, S2 and S3, S3 and S4, and S4 and S5, respectively. Total body haptoglobin (TBH) was estimated from Hapt and % PVC in an attempt to correct for the plasma volume change effect on haptoglobin concentration.(ABSTRACT TRUNCATED AT 250 WORDS)