Many adverse environmental and genetic factors can affect stability of development during human growth. Although the level of fluctuating asymmetry (FA) may be influenced by environmental and genetic stress encountered during this period, directional asymmetry (DA) is largely attributable to differential mechanical loading during bone growth, for example, handedness. I assessed the effects of heavy working conditions and socioeconomic conditions on asymmetry levels in three groups of young human males: 1) individuals employed in the heavy industry sector (n = 104, mean age = 18.48 +/- 0.61 years), 2) individuals who had the same socioeconomic status as the laborers (n = 102, mean age = 18.39 +/- 0.58 years) but were not laborers, and 3) nonlaborers from the higher socioeconomic levels of society (n = 103, mean age = 18.43 +/- 0.67). For all subjects, hand length, hand width, elbow width, wrist width, knee width, ankle width, foot length, foot width, ear length, and ear width were measured. All measurements of the upper extremities in the labor group appeared to exhibit DA; in the other two groups only hand measurements exhibited DA. According to analysis of FA, subjects living in poor conditions exhibited more FA than their nonlaborer peers living in better conditions. In addition, biomechanical pressures due to heavy working conditions of the labor group appeared to cause increased DA in the upper extremities: DA increased with an increase in the number of years working. Am J Phys Anthropol 143:112-120, 2010. (C) 2010 Wiley-Liss, Inc.