The claim by Trivers and Hare (1976) and Nonacs (1986) that the ratio of sexual investment in monogynous ants is as much female-biased as 3:1 on the average is untenable because of 1) bias in the gyne-to-male dry-weight cost ratios, as a result of increasingly diverging rates of respiration and fat accumulation with increasing sexual dimorphism; and 2) bias in the numerical sex ratios estimated from small samples. Partial regressions of the numerical gyne-to-male sex ratio on the individual dry-weight ratio and sample size appeared to be consistently present in the data sets for monogynous and polygynous ants, although significantly so only for monogynous ants. These relationships were primarily interpreted as methodological artifacts, but possible biological explanations are also discussed. After adjustment for the assumed artifacts, the geometric-mean investment ratio across monogynous ants was estimated to be 1.82:1 in favor of gynes. -from Author