The purpose was to determine if solderers had increased diurnal variation (DV) in peak expiratory flow rate (PEFR) and chronic impairment of lung function. A cross-sectional study of 150 female operators doing manual soldering using flux-cored (rosin-based) solder wire and 52 administrative staff from two electronics factories was carried out. They answered a questionnaire, had their forced expiratory volume in 1 sec (FEV1) and forced vital capacity (FVC) measured and their 3-hourly PEFR monitored for 5 working days. The DV in PEFR was the difference in the daily maximum and minimum PEFR expressed as a percentage of the maximum. Six solderers with smoking history were excluded from the analysis. Solderers had a significantly higher prevalence of work-related eye (14.6%) and nose (10.4%) irritation. The prevalence of cough, breathlessness, and wheezing was low. There was no overt case of occupational asthma. The DV in PEFR of 6.0% was not increased. The analysis of FEV1 and FVC was restricted to Chinese only (101 solderers and 51 controls): these were not significantly different. Solderers with 5 or more years of exposure had a significantly lower FEV1/FVC (%) of 88.4% after adjustment for age. In conclusion, solderers with 5 or more years of exposure may have a mild obstructive effect apart from smoking, asthma, or age.