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Embryogenic callus growth of sweetpotato (Ipomoea batatas (L.) Lam.) was selectively enhanced by subculture on basal callus proliferation medium modified to contain 15 m M NH4NO3. Embryogenic callus production was doubled on basal callus proliferation medium modified to contain 60 m M K+, while nonembryogenic callus production was reduced 40%. Additions of up to 40 mM NaCl to basal callus proliferation medium did not affect callus proliferation. The development of embryos from calli subculture to embryo production basal medium was unaffected by the KCl or NaCl treatments of the callus proliferation phase. However, embryo production was increased by subculturing callus from callus proliferation medium containing 20 m M to embryo production medium containing 10 m M Our results demonstrate that changes in mineral nutrition, in addition to growth regulator differences between callus proliferation and embryo production media, are important factors in sweetpotato somatic embryogenesis. Clonal propagation via somatic embryogenesis has been pro- posed by Cantliffe et al. (1988) for synthetic seed production of sweetpotato. Sweetpotato somatic embryo production is ac- complished in two stages (Chee and Cantliffe, 1988a). Embry- ogenic callus is continuously proliferated by subculture on media containing growth regulators; embryos are produced by trans- ferring embryogenic callus to media without growth regulators. Formation of embryogenic callus was enhanced by addition of 10 µM (2,4-dichlorophenoxy)acetic acid (2,4-D) and 1 µ M N- (phenylmethyl)-1 H- purine-6-amine (BA) (Chee and Cantliffe, 1988b). Further improvements in embryogenic callus growth and embryo production could be expected by optimizing in- organic salts in the basal medium. However, information on the mineral nutrition of embryogenic callus is insufficient (Ammir- ato, 1983; Vasil, 1984). Nitrogen is quantitatively the major mineral nutrient taken up during growth of plant tissues (Marschner, 1986). Supplying N in its reduced rather than oxidized form to tissue culture likely would be more efficient for growth, since NO3 reduction is energetically expensive (Clarkson and Hanson, 1980). How- ever, cultured cells were unable to grow on as the sole N source when media did not include organic acids as buffers, or without continuous titration of the medium (Chaleff, 1983; Dou- gall and Verma, 1978; Fukunaga et al., 1978; Gamborg and Shyluk; 1970; Martinet al., 1977). This result is to be expected since uptake is physiological ly acidic (Marschner, 1986). The relative and absolute amounts of also in- fluence embryogenesis in cell cultures (Tazawa and Reinert, 1969). Generally, it is thought that the ionic form of N affects growth and nutrient uptake by altering cation-anion balance, changing organic anion accumulation and ultimately affecting medium and cytosol pH values (Marschner, 1986; Poole, 1978