Using a relative rate method with in situ generation of the hydroxyaldehydes, rate constants for the reactions of the OH radical with 2-hydroxybutanal [CH3CH2CH(OH)CHO], 3-hydroxybutanal [CH3CH(OH)CH2CHO], 2-hydroxypropanal [CH3CH(OH)CHO], 2-hydroxy-2-methylpropanal [(CH3)(2)C(OH)CHO], and 3-hydroxypropanal [HOCH2CH2CHO] have been measured at atmospheric pressure and 296 +/- 2 K. The hydroxyaldehydes were generated in situ from the OH radical-initiated reactions of precursor compounds (1,2- and 1,3-butanediol, 2-methyl-2,4-pentanediol, 2-methyl-3-buten-2-ol, and cis-3-hexen-1-ol) and the rate constants for the reaction of OH radicals with the hydroxyaldehydes were determined relative to those for reaction of OH radicals with the precursor compound. The rate constants obtained (in units of 10(-11) cm(3) molecule(-1) s(-1)) were CH3CH2CH(OH)CHO, 2.37 +/- 0.23; CH3CH(OH)CH2CHO, 2.95 +/- 0.24; CH3CH(OH)CHO, 1.70 +/- 0.20; (CH3)(2)C(OH)CHO, 1.40 +/- 0.25; and HOCH2CH2CHO, 1.99 +/- 0.29.