The present invention provides pegylated hemoglobins comprising a thiocarbamoyl-phenyl-polyethylene glycol (PEG) attached to hemoglobin, and comprising a polyethylene glycol (PEG) attached to hemoglobin by an acyl group. The invention also provides methods of preparing pegylated hemoglobins using isothiocyanato phenyl carbamate of PEG and using isothiocyanato phenyl di-PEG carbamate. The invention further provides compositions and blood substitutes comprising pegylated hemoglobins and methods of treating a subject which comprise administering to the subject blood substitutes comprising non-hypertensive pegylated hemoglobins.