The autotetraploid plants of the cultivated tomato Lycopersicon esculentum 'Lukullus' differed from their diploid progenitors by lower RNA and protein contents, expressed as either per unit fresh weight or per unit DNA. The DNA content per unit fresh weight was similar in both plant types. Under salinity, DNA content decreased in both plant types similarly; RNA level was practically unchanged, whereas protein level per unit DNA increased in both types but more so in the polyploids. Compared with the diploid plants, the polyploids, under both control and saline conditions, had lower values of RNase activity, uptake and incorporation of labeled leucine, and abscisic acid content. Under salinity, both plant types had increased RNase activity and abscisic acid content but decreased leucine uptake and incorporation.