Two stalagmites, SAN-H and TABI-I were collected from caves in the northern Yucatan Peninsula to analyze for the stable isotopes of carbon and oxygen. The δ¹³C value can be used to determine whether C₃ or C₄/CAM vegetation was dominant and the δ ¹⁸O value can theoretically be used to determine whether the climate was wet or arid. Samples were cut, polished, dated using U/Th dating, and sampled using a micromill. SAN-H was dated as Early Classic (1650-1350 B.P.) to the Middle Preclassic 2850-2250 B.P) and the δ¹³C and δ¹⁸O appears to reinforce the interpretations from similar studies. The range of isotope values for δ¹⁸O and δ¹³C were -2.3 to -5.5‰ and -4.0 to -10.3‰, respectively. Although the U/Th dates for TABI-I range from Historical to Late Classic(1350-1050 B.P.), the early Late Classic date is almost certainly invalid, and is the result of presence of clastic material in the sample. TABI-I's range of isotope values for δ¹⁸O and δ ¹³C were –2.1 to -4.9‰ and –4.7 to -9.6‰, respectively. TABI-I's δ¹⁸O values appear to be supportive of interpretations found in the literature based on lakecore, stalagmite and sediment studies, and δ¹³C values could be informative about possible vegetation and land use in the immediate vicinity. Problems with dating reversal and dating accuracy prevented more detailed interpretations of the data.