Data reported in the literature up to 1985 on reciprocal translocation induction in male mouse germ cells by external gamma-ray doses ranging from 0.5 to 6.0 Gy delivered at fixed dose rates were analyzed. On the assumption of a non-threshold linear dose response, zero effect at zero dose, and a center of distribution lying on an approximately straight line, calculations were made of linear regression coefficients. These coefficients (b), as a function of the dose rate (P), were well fitted by two straight lines: b = (3.15 +/- 0.59 log P) X 10(-6) for dose rates from 0.01 to 0.1 mGy/min; and b = (7.52 +/- 3.86 log P) X 10(-6) for dose rates ranging from 0.06 to 1.2 X 10(3) mGy/min. The intersection point of these two lines determined the so-called threshold level of the dose rate, namely, 4.6 X 10(-2) mGy/min, at which the effectiveness of external gamma-irradiation is not expected to exceed 2.36 X 10(-6)/mGy. In addition, experiments were undertaken in which yields were recorded of reciprocal translocations in germ cells of male mice exposed to 0.9 Gy of gamma-radiation at dose rates ranging from 6.14 X 10(-3) to 6.14 X 10(2) mGy/min (6 levels); comparisons were made with data published up to 1985 from similar studies using other fixed doses. To do this, translocation yields were expressed as relative yields (F) and their relationship to the dose rate (P) for the individual fixed doses was represented by an equation of the type: F = alpha + beta log P. For most of the equations, the regression coefficients were in good agreement and a single relationship was obtained to represent them. From the analysis performed it follows that, within the 0.6-6.0 Gy dose range, the pattern of the F vs. P relationship is unaffected by the dose. This supports the initial assumption that for the dose range up to 6.0 Gy the dose response for the reciprocal translocation yield is a non-threshold straight-line relationship.