BACKGROUND: Laboratory work may constitute a possible health hazard for workers as well as for their offspring, and involves a wide range of exposures, such as organic solvents, carcinogenic agents, ionizing radiation, and/or microbiological agents. Adverse pregnancy outcomes in the offspring of male employees in biomedical research laboratories are examined. METHODS: Offspring to males employed 1970-1989 at four Swedish universities were identified via the Medical Birth Register (MBR), along with other pregnancy parameters. Offspring of fathers with laboratory work (n = 2,281) is considered exposed, and of non-laboratory employees unexposed (n = 1,909). Exposure data were obtained by questionnaires to research group leaders. Logistic regression analysis estimated odds ratios (ORs) and 95% confidence intervals (CIs). RESULTS: Paternal laboratory work in general showed no statistically significant increased ORs concerning birth weight and/or gestational age, but work specifically with radioactive isotopes gave OR 1.8 (CI 1.0-3.2) for high birth weight and a relative risk of 1.2 (CI 1.0-1.4) for sex ratio (male/female). CONCLUSIONS: There was no clear association between periconceptional paternal laboratory work and adverse reproductive outcomes, but use of radioactive isotopes showed increased OR for high birth weight in offspring.